LTC3558EUD-PBF_技术文档

LTC3558

Linear USB Battery Charger

with Buck and

Buck-Boost Regulators

FEATURES

DESCRIPTION

The LTC^®3558 is a USB battery charger with dual high ef-

ﬁciency switching regulators. The device is ideally suited

to power single-cell Li-Ion/Polymer based handheld ap-

plications needing multiple supply rails.

Battery Charger

n

Standalone USB Charger

n

Up to 950mA Charge Current Programmable via

Single Resistor

n

HPWR Input Selects 20% or 100% of Programmed

Battery charge current is programmed via the PROG pin

and the HPWR pin with capability up to 950mA of current

at the BAT pin. The CHRG pin allows battery status to be

monitored continuously during the charging process. An

internal timer controls charger termination.

Charge Current

n

NTC Input for Temperature Qualiﬁed Charging

n

Internal Timer Termination

Bad Battery Detection

n

Switching Regulators (Buck and Buck-Boost)

Thepartincludesmonolithicsynchronousbuckandbuck-

boost regulators that can provide up to 400mA of output

current each and operate at efﬁciencies greater than 90%

over the entire Li-Ion/Polymer battery range. The buck-

boostregulatorcanregulateitsprogrammedoutputvoltage

at its rated deliverable current over the entire Li-Ion range

without drop out, increasing battery runtime.

n

Up to 400mA Output Current per Regulator

n

2.25MHz Constant-Frequency Operation

Power Saving Burst Mode^®Operation

n

Low Proﬁle, 20-Lead, 3mm × 3mm QFN Package

APPLICATIONS

TheLTC3558isofferedinalowproﬁle(0.75mm),thermally

enhanced, 20-lead (3mm × 3mm) QFN package.

, LT, LTC, LTM and Burst Mode are registered trademarks of Linear Technology

Corporation. All other trademarks are the property of their respective owners.

n

SD/Flash-Based MP3 Players

Low Power Handheld Applications

n

TYPICAL APPLICATION

USB Charger Plus Buck Regulator and Buck-Boost Regulator

Demo Board

USB (4.3V TO 5.5V)

V

BAT

CC

SINGLE

Li-lon CELL

(2.7V TO 4.2V)

+

1μF

PV

IN1

IN2

PV

1.74k

PROG

NTC

10μF

1.2V AT 400mA

SW1

4.7μH

LTC3558

10pF

10μF

324k

649k

CHRG

SUSP

HPWR

MODE

EN1

FB1

SWAB2

2.2μH

3.3V AT 400mA

DIGITAL

CONTROL

SWCD2

V

OUT2

121k

22μF

324k

105k

33pF

EN2

FB2

15k

330pF

10pF

EXPOSED

PAD

GND

V

C2

3558 TA01

3558f

1

LTC3558

ABSOLUTE MAXIMUM RATINGS

PIN CONFIGURATION

(Note 1)

V

(Transient);

TOP VIEW

CC

t < 1ms and Duty Cycle < 1%....................... –0.3V to 7V

(Static) .................................................. –0.3V to 6V

V

CC

20 19 18 17 16

BAT, CHRG ................................................... –0.3V to 6V

EN2

15

14

13

12

11

GND

BAT

1

2

3

4

5

V

PROG, SUSP.................................–0.3V to (V + 0.3V)

C2

CC

FB2

21

8

MODE

FB1

HPWR, NTC...................–0.3V to Max (V , BAT) + 0.3V

CC

SUSP

PROG Pin Current...............................................1.25mA

V

EN1

OUT2

BAT Pin Current ..........................................................1A

6

7

9 10

PV , PV ..................................–0.3V to (BAT + 0.3V)

IN1

IN2

EN1, EN2, MODE, V

.............................. –0.3V to 6V

OUT2

UD PACKAGE

20-LEAD (3mm × 3mm) PLASTIC QFN

FB1, SW1......................... –0.3V to (PV + 0.3V) or 6V

IN1

FB2, V , SWAB2............. –0.3V to (PV + 0.3V) or 6V

C2

IN2

OUT2

T

= 125°C, θ = 68°C/W

JA

JMAX

SWCD2 ............................–0.3V to (V

+ 0.3V) or 6V

EXPOSED PAD (PIN 21) IS GND, MUST BE SOLDERED TO PCB

I

...............................................................600mA DC

SW1

, I

...................................750mA DC

SWAB2 SWCD2 VOUT2

Junction Temperature (Note 2) ............................. 125°C

Operating Temperature Range (Note 3).... –40°C to 85°C

Storage Temperature.............................. –65°C to 125°C

ORDER INFORMATION

LEAD FREE FINISH

TAPE AND REEL

PART MARKING

PACKAGE DESCRIPTION

20-Lead (3mm × 3mm) Plastic QFN

TEMPERATURE RANGE

–40°C to 85°C

LTC3558EUD#PBF

LTC3558EUD#TRPBF

LDCD

Consult LTC Marketing for parts speciﬁed with wider operating temperature ranges.

Consult LTC Marketing for information on non-standard lead based ﬁnish parts.

For more information on lead free part marking, go to: http://www.linear.com/leadfree/

For more information on tape and reel speciﬁcations, go to: http://www.linear.com/tapeandreel/

3558f

2

LTC3558

ELECTRICAL CHARACTERISTICS ^Thel denotes speciﬁcations that apply over the full operating temperature

range, otherwise speciﬁcations are at T_A= 25°C. V_CC= 5V, BAT = PV_IN1= PV_IN2= 3.6V, R_PROG= 1.74k, unless otherwise noted.

SYMBOL

PARAMETER

CONDITIONS

MIN

TYP

MAX

UNITS

Battery Charger

l

V

Input Supply Voltage

4.3

5.5

V

CC

I

Battery Charger Quiescent Current

(Note 4)

Standby Mode, Charge Terminated

285

8.5

400

17

μA

VCC

Suspend Mode, V

= 5V

SUSP

V

BAT Regulated Output Voltage

4.179

4.165

440

84

4.200

460

92

–3.5

–2.5

–1.5

4.221

4.235

500

100

–7

–4

–3

V

mA

μA

FLOAT

CHG

0°C ≤ T ≤ 85°C

HPWR = 1

HPWR = 0

A

l

I

Constant-Current Mode Charge

Current

Battery Drain Current

Standby Mode, Charger Terminated, EN1 = EN2 = 0

Shutdown, V < V , BAT = 4.2V, EN1 = EN2 = 0

BAT

CC

UVLO

Suspend Mode, SUSP = 5V, BAT = 4.2V, EN1 = EN2 = 0

= 0V, EN1 = EN2 = 1, MODE = 1,

V

CC

FB1 = FB2 = 0.85V, V

= 3.6V

–50

4

–100

4.125

μA

V

OUT2

V

UVLO

Undervoltage Lockout Threshold

Undervoltage Lockout Hysteresis

BAT = 3.5V, V Rising

3.85

30

CC

BAT = 3.5V

200

50

mV

ΔV

UVLO

V

Differential Undervoltage Lockout

Threshold

BAT = 4.05V, (V – BAT) Falling

70

DUVLO

CC

Differential Undervoltage Lockout

Hysteresis

BAT = 4.05V

130

mV

ΔV

DUVLO

V

PROG

PROG Pin Servo Voltage

HPWR = 1

HPWR = 0

1.000

0.200

0.100

V

BAT < V

TRKL

h

PROG

Ratio of I to PROG Pin Current

800

mA/mA

BAT

I

Trickle Charge Current

BAT < V

36

46

56

3

mA

TRKL

V

Trickle Charge Threshold Voltage

Trickle Charge Hysteresis Voltage

Recharge Battery Threshold Voltage

Recharge Comparator Filter Time

Safety Timer Termination Period

Bad Battery Termination Time

BAT Rising

2.8

2.9

100

–95

1.7

4

V

TRKL

mV

ΔV

TRKL

Threshold Voltage Relative to V

BAT Falling

–75

–115

mV

FLOAT

RECHRG

t

ms

RECHRG

BAT = V

3.5

0.4

4.5

0.6

Hour

mA/mA

ms

TERM

FLOAT

TRKL

BAT < V

0.5

0.1

2.2

500

BADBAT

h

End-of-Charge Indication Current Ratio (Note 5)

0.085

0.11

C/10

t

End-of-Charge Comparator Filter Time

I

Falling

BAT

R

Battery Charger Power FET On-

Resistance (Between V and BAT)

I

= 190mA

mΩ

ON(CHG)

CC

T

Junction Temperature in Constant

Temperature Mode

105

°C

LIM

NTC

V

Cold Temperature Fault Threshold

Voltage

Hot Temperature Fault Threshold

Voltage

Rising NTC Voltage

Hysteresis

Falling NTC Voltage

Hysteresis

Falling NTC Voltage

Hysteresis

75

33.4

0.7

–1

76.5

1.6

34.9

1.6

1.7

50

78

36.4

2.7

1

%V

%V_CC

%V

CC

mV

μA

COLD

HOT

DIS

CC

l

NTC Disable Threshold Voltage

I

NTC Leakage Current

V = V = 5V

NTC CC

NTC

3558f

3

LTC3558

ELECTRICAL CHARACTERISTICS ^Thel denotes speciﬁcations that apply over the full operating temperature

range, otherwise speciﬁcations are at T_A= 25°C. V_CC= 5V, BAT = PV_IN1= PV_IN2= 3.6V, R_PROG= 1.74k, unless otherwise noted.

SYMBOL

PARAMETER

CONDITIONS

MIN

TYP

MAX

UNITS

Logic (HPWR, SUSP, CHRG, EN1, EN2, MODE)

V

Input Low Voltage

HPWR, SUSP, MODE, EN1, EN2 Pins

HPWR, SUSP Pins

0.4

V

IL

Input High Voltage

1.2

1.9

IH

l

R

Logic Pin Pull-Down Resistance

CHRG Pin Output Low Voltage

CHRG Pin Input Current

4

100

0

6.3

250

1

MΩ

mV

μA

DN

V

I

= 5mA

CHRG

I

BAT = 4.5V, V

= 5V

CHRG

Buck Switching Regulator

l

PV

Input Supply Voltage

2.7

4.2

V

IN1

I

Pulse Skip Input Current

Burst Mode Current

Shutdown Current

FB1 = 0.85V, MODE = 0 (Note 6)

FB1 = 0.85V, MODE = 1 (Note 6)

EN1 = 0

220

35

0

400

50

2

μA

PVIN1

Supply Current in UVLO

PV = PV = 2V

4

8

IN1

IN2

l

PV UVLO

PV Falling

IN1

Switching Frequency

Peak PMOS Current Limit

Feedback Voltage

2.30

2.45

2.55

2.25

800

V

IN1

PV Rising

2.70

2.59

f

I

MODE = 0

1.91

550

780

–50

100

MHz

mA

mV

nA

%

OSC

1050

820

50

LIMSW1

l

V

FB1

I

FB Input Current

FB1 = 0.85V

FB1 = 0V

D

R

Maximum Duty Cycle

MAX1

R

of PMOS

of NMOS

I

= 100mA

0.65

0.75

13

Ω

PMOS1

NMOS1

SW1(PD)

DS(ON)

SW1

= –100mA

Ω

SW Pull-Down in Shutdown

kΩ

Buck-Boost Switching Regulator

l

PV

IN2

Input Supply Voltage

2.7

4.2

V

I

PWM Input Current

MODE = 0, I

MODE = 1, I

= 0A, FB2 = 0.85V (Note 6)

220

20

0

400

30

1

μA

PVIN2

OUT

Burst Mode Input Current

Shutdown Current

EN2 = 0, I

= 0A

OUT

Supply Current in UVLO

PV = PV = 2V

4

8

IN1

IN2

l

PV UVLO

PV Falling

IN2

Minimum Regulated Buck-Boost V

2.30

2.45

2.55

V

IN2

PV Rising

2.70

2.75

V

2.65

5.60

700

250

450

0

OUT2(LOW)

OUT2(HIGH)

LIMF2

OUT

Maximum Regulated Buck-Boost V

Forward Current Limit (Switch A)

Reverse Current Limit (Switch D)

5.45

580

180

325

–35

50

V

OUT

l

I

MODE = 0

MODE = 1

MODE = 0

MODE = 1

820

320

575

35

mA

PEAK2(BURST)

LIMR2

ZERO2(BURST)

MAX2(BURST)

Maximum Deliverable Output Current

in Burst Mode Operation

2.7V < PV < 4.2V

IN2

2.75V < V

< 5.5V

OUT2

l

V

Feedback Servo Voltage

780

–50

1.91

800

820

50

mV

nA

FB2

I

f

FB2 Input Current

FB2 = 0.85V

MODE = 0

FB2

Switching Frequency

2.25

2.59

MHz

OSC

3558f

4

LTC3558

ELECTRICAL CHARACTERISTICS ^Thel denotes speciﬁcations that apply over the full operating temperature

range, otherwise speciﬁcations are at T_A= 25°C. V_CC= 5V, BAT = PV_IN1= PV_IN2= 3.6V, R_PROG= 1.74k, unless otherwise noted.

SYMBOL

PARAMETER

CONDITIONS

= 3.6V

MIN

TYP

MAX

UNITS

Ω

R

PMOS R

V

OUT

0.6

DSP(ON)

DS(ON)

R

NMOS R

0.6

Ω

DSN(ON)

DS(ON)

I

PMOS Switch Leakage

NMOS Switch Leakage

Maximum Buck Duty Cycle

Maximum Boost Duty Cycle

Soft-Start Time

Switches A, D

Switches B, C

MODE = 0

–1

1

μA

%

LEAK(P)

LEAK(N)

l

DC

100

BUCK(MAX)

MODE = 0

75

0.5

10

%

BOOST(MAX)

t

ms

SS2

R

V

Pull-Down in Shutdown

OUT

kΩ

OUT(PD)

Note 1: Stresses beyond those listed under Absolute Maximum Ratings

may cause permanent damage to the device. Exposure to any Absolute

Maximum Rating condition for extended periods may affect device

reliability and lifetime.

Note 4: V supply current does not include current through the PROG pin

or any current delivered to the BAT pin. Total input current is equal to this

CC

speciﬁcation plus 1.00125 • I where I is the charge current.

BAT

Note 5: I

is expressed as a fraction of measured full charge current

C/10

Note 2: T is calculated from the ambient temperature T and power

with indicated PROG resistor.

J

A

dissipation P according to the following formula:

D

Note 6: Dynamic supply current is higher due to the gate charge being

T = T + (P • θ )

JA

delivered at the switching frequency.

J

A

D

Note 3: The LTC3558E is guaranteed to meet speciﬁcations from 0°C to

85°C. Speciﬁcations over the –40°C to 85°C operating temperature range

are assured by design, characterization and correlation with statistical

process controls.

3558f

5

LTC3558

TYPICAL PERFORMANCE CHARACTERISTICS ^T_A^{= 25°C, unless otherwise noted.}

Battery Regulation (Float) Voltage

vs Battery Charge Current,

Constant-Voltage Charging

Suspend State Supply and BAT

Currents vs Temperature

Battery Regulation (Float)

Voltage vs Temperature

10

9

8

7

6

5

4

3

2

1

0

4.24

4.205

4.200

4.195

4.190

4.185

4.180

4.175

4.170

4.165

4.160

4.155

4.150

V

= 5V

CC

4.23

4.22

I

VCC

4.21

4.20

4.19

4.18

4.17

V

= 5V

CC

BAT = 4.2V

SUSP = 5V

EN1 = EN2 = 0V

V

= 5V

CC

I

BAT

HPWR = 5V

R

= 845Ω

PROG

EN1 = EN2 = 0V

4.16

–55

–15

5

25

45

65

85

–35 –15

25

45

65

85

–35

–55

5

0

100 200 300 400 500 600 700 800 9001000

TEMPERATURE (°C)

I

(mA)

BAT

3558 G01

3558 G02

3558 G03

Battery Charge Current vs Ambient

Temperature in Thermal Regulation

Battery Charge Current

vs Supply Voltage

Battery Charge Current

vs Battery Voltage

500

495

490

485

480

475

470

465

460

455

450

445

440

500

450

400

350

300

250

200

150

100

50

500

450

400

350

300

250

200

150

100

50

V

= 5V

HPWR = 5V

V

= 5V

PROG

CC

HPWR = 5V

= 1.74k

R

= 1.74k

R

PROG

EN1 = EN2 = 0V

V

= 5V

HPWR = 0V

3.5

CC

HPWR = 5V

= 1.74k

R

PROG

EN1 = EN2 = 0

0

4.3 4.4

4.6

4.8 4.9 5.0 5.1 5.2 5.3 5.4 5.5

4.7

4.5

–55 –35 –15

5

25 45 65 85 105 125

2

2.5

3

4

4.5

V

(V)

TEMPERATURE (°C)

CC

V

(V)

BAT

3558 G04

3558 G06

3558 G05

Battery Drain Current in Undervoltage

Lockout vs Temperature

Battery Charger Undervoltage

PROG Voltage

Lockout Threshold vs Temperature

vs Battery Charge Current

1.2

1.0

4.2

4.1

3.0

2.5

2.0

1.5

V

= 5V

BAT = 3.5V

CC

EN1 = EN2 = 0V

HPWR = 5V

= 1.74k

R

PROG

RISING

EN1 = EN2 = 0V

BAT = 4.2V

4.0

3.9

3.8

3.7

3.6

0.8

0.6

BAT = 3.6V

FALLING

0.4

0.2

0

1.0

0.5

0

3.5

0

50 100 150 200 250 300 350 400 450 500

(mA)

25

TEMPERATURE (°C)

65

85

–55 –35 –15

5

45

25

TEMPERATURE (°C)

65

85

–55 –35 –15

5

45

I

BAT

3558 G09

3558 G07

3558 G08

3558f

6

LTC3558

TYPICAL PERFORMANCE CHARACTERISTICS

T_A= 25°C, unless otherwise noted.

Recharge Threshold

vs Temperature

Battery Charger FET

SUSP/HPWR Pin Rising

On-Resistance vs Temperature

Thresholds vs Temperature

115

111

107

103

99

1.2

700

650

600

550

500

450

400

350

300

V

= 5V

V

= 5V

V

BAT

EN1 = EN2 = 0V

= 4V

CC

I

= 200mA

1.1

1.0

0.9

0.8

0.7

0.6

0.5

95

91

87

83

79

75

0.4

–55

–15

5

25

45

65

85

–55

–35 –15

5

25

45

65

85

–35

–15

5

25

45

65

85

–55 –35

TEMPERATURE (°C)

3558 G10

3558 G12

3558 G11

CHRG Pin Output Low Voltage

vs Temperature

CHRG Pin I-V Curve

Timer Accuracy vs Supply Voltage

140

120

2.0

1.5

1.0

0.5

0

70

60

50

40

30

20

10

0

V

I

= 5V

CHRG

V

= 5V

CC

= 5mA

BAT = 3.8V

100

80

60

40

20

–0.5

–1.0

0

25

TEMPERATURE (°C)

65

85

–55 –35 –15

5

45

4.3

4.7

4.9

(V)

5.1

5.3

5.5

4.5

4

6

0

1

2

3

5

V

CC

CHRG (V)

3558 G13

3558 G15

3558 G14

Complete Charge Cycle

2400mAh Battery

Buck and Buck-Boost Regulator

Switching Frequency vs Temperature

Timer Accuracy vs Temperature

2.425

2.325

2.225

2.125

2.025

1.925

1.825

1.725

7

6

1000

800

600

400

200

0

5.0

4.5

4.0

3.5

3.0

5.0

4.0

3.0

2.0

1.0

0

V

= 5V

V

= 0V, MODE = 0

CC

V

= 5V

CC

PROG

BAT = PV = PV

IN1

IN2

R

= 0.845k

HPWR = 5V

5

BAT = 4.2V

BAT = 3.6V

4

BAT = 2.7V

3

2

1

0

–1

–2

–55 –35 –15

5

25 45 65 85 105 125

–55 –35 –15

5

85

0

1

2

3

4

5

6

25

45

65

TEMPERATURE (°C)

TIME (HOUR)

3558 G17

3558 G18

3558 G16

3558f

7

LTC3558

TYPICAL PERFORMANCE CHARACTERISTICS ^T_A^{= 25°C, unless otherwise noted.}

Buck and Buck-Boost Regulator

Undervoltage Thresholds

vs Temperature

Buck and Buck-Boost Regulator

Enable Thresholds

Buck Regulator Input Current vs

Temperature, Burst Mode Operation

vs Temperature

1200

1100

1000

900

2.750

2.700

2.650

2.600

2.550

2.500

2.450

2.400

2.350

2.300

2.250

50

45

BAT = PV = PV = 3.6V

BAT = PV = PV

FB1 = 0.85V

IN1

IN2

IN1

IN2

RISING

40

PV = 4.2V

IN1

800

35

30

FALLING

RISING

PV = 2.7V

IN1

700

FALLING

600

25

20

500

400

–55 –35 –15

5

25 45 65 85 105 125

–55 –35 –15

5

25 45 65 85 105 125

–55 –35 –15

5

25 45 65 85 105 125

TEMPERATURE (°C)

3558 G20

3558 G19

3558 G21

Buck Regulator Input Current vs

Temperature, Pulse Skip Mode

Buck Regulator PMOS R_DS(0N)

vs Temperature

Buck Regulator NMOS R_DS(0N)

vs Temperature

1300

1200

1100

1000

900

1300

1200

1100

1000

900

400

350

FB1 = 0.85V

300

PV = 2.7V

IN1

PV = 4.2V

IN1

250

200

PV = 2.7V

IN1

800

PV = 2.7V

IN1

PV = 4.2V

IN1

PV = 4.2V

IN1

700

600

150

100

500

400

–55 –35 –15

5

25 45

125

–55 –35 –15

5

25 45

125

65 85 105

–55 –35 –15

5

25 45 65 85 105 125

TEMPERATURE (°C)

3558 G23

3558 G24

3558 G22

Buck Regulator Efﬁciency vs I_LOAD

Buck Regulator Load Regulation

Buck Regulator Line Regulation

100

90

80

70

60

50

40

30

20

10

0

1.250

1.240

1.230

1.220

1.210

1.200

1.190

1.180

1.170

1.160

1.150

1.25

1.24

1.23

1.22

I

= 200mA

LOAD

PV = 3.6V

IN1

OUT

Burst Mode

OPERATION

V

= 1.2V

Burst Mode

OPERATION

1.21

1.20

PULSE SKIP

MODE

PULSE SKIP

MODE

1.19

1.18

1.17

1.16

1.15

V

= 1.2V

OUT

PV = 2.7V

IN1

PV = 4.2V

IN1

0.1

1

10

(mA)

100

1000

2.700

3.000

3.300

3.600

3.900

4.200

1

10

100

1000

I

PV (V)

IN1

LOAD

I

(mA)

LOAD

3558 G25

3558 G27

3558 G26

3558f

8

LTC3558

TYPICAL PERFORMANCE CHARACTERISTICS ^T_A^{= 25°C, unless otherwise noted.}

Buck Regulator

Pulse Skip Mode Operation

Buck Regulator

Burst Mode Operation

Buck Regulator Start-Up Transient

V

OUT

V

OUT

V

OUT

20mV/

500mV/DIV

DIV (AC)

SW

INDUCTOR

CURRENT

SW

2V/DIV

I

= 200mA/

DIV

L

INDUCTOR

CURRENT

= 50mA/

DIV

INDUCTOR

CURRENT

= 60mA/

DIV

EN

2V/DIV

I

L

I

L

3558 G29

3558 G28

3558 G30

PV = 3.8V

IN1

LOAD = 10mA

200ns/DIV

PV = 3.8V

IN1

50μs/DIV

PULSE SKIP MODE

LOAD = 6Ω

PV = 3.8V

IN1

LOAD = 60mA

2μs/DIV

Buck Regulator Transient

Response, Pulse Skip Mode

Buck Regulator Transient

Response, Burst Mode Operation

Buck-Boost Regulator Input

Current vs Temperature

30

25

20

15

10

5

INDUCTOR

CURRENT

INDUCTOR

CURRENT

Burst Mode OPERATION

FB2 = 0.85V

I = 200mA/

I

= 200mA/

L

DIV

PV = 4.2V

IN2

V

OUT

V

OUT

50mV/

PV = 2.7V

IN2

DIV (AC)

LOAD STEP

5mA TO

290mA

LOAD STEP

5mA TO

290mA

3558 G32

3558 G31

PV = 3.8V

IN1

50μs/DIV

PV = 3.8V

IN1

50μs/DIV

–55 –35 –15

5

25 45 65 85 105 125

TEMPERATURE (°C)

3558 G33

Buck-Boost Regulator NMOS

R_DS(ON)vs Temperature

Buck-Boost Regulator Input

Current vs Temperature

Buck-Boost Regulator PMOS

R_DS(ON)vs Temperature

500

450

400

350

300

250

200

150

100

800

750

700

650

600

550

500

450

400

350

300

250

200

1200

1100

1000

900

800

700

600

500

400

300

200

PWM MODE

FB2 = 0.85V

PV = 2.7V

IN2

PV = 2.7V

IN2

PV = 4.2V

IN2

PV = 4.2V

IN2

PV = 2.7V

IN2

PV = 4.2V

IN2

–55 –35 –15

5

25 45 65 85 105 125

–55 –35 –15

5

45

85 105 125

25

65

85

105 125

–55 –35 –15

5

25 45 65

TEMPERATURE (°C)

3558 G35

3558 G34

3558 G36

3558f

9

LTC3558

TYPICAL PERFORMANCE CHARACTERISTICS

T_A= 25°C, unless otherwise noted.

Buck-Boost Efﬁciency

vs Load Current

Buck-Boost Regulator

Efﬁciency vs Input Voltage

100

90

80

70

60

50

40

30

20

100

95

90

85

80

75

70

65

60

55

50

V

= 3.3V

V

= 3.3V

OUT

I

= 10mA

LOAD

I

= 1mA

3.6V

4.2V

LOAD

2.7V

I

= 100mA

LOAD

I

= 400mA

LOAD

2.7V

Burst Mode

OPERATION

PWM MODE

PV , Burst Mode

IN2

3.6V

4.2V

OPERATION

10

0

0.10

PV , PWM MODE

IN2

2.700

3.000

3.300

3.600

3.900

4.200

1

10

(mA)

100

1000

I

PV (V)

IN2

LOAD

3558 G37

3558 G38

Buck-Boost Regulator

Load Regulation

Buck-Boost Regulator

Line Regulation

3.36

3.35

3.34

3.33

3.32

3.31

3.30

3.29

3.28

3.27

3.26

3.25

3.24

3.36

3.35

3.34

3.33

3.32

3.31

3.30

3.29

3.28

3.27

3.26

3.25

3.24

PV = 3.6V

IN2

Burst Mode OPERATION

PWM MODE

I

= 100mA

LOAD

PWM MODE

Burst Mode

OPERATION

I

= 10mA

LOAD

2.700

3.000

3.300

3.600

3.900

4.200

0.10

1

10

(mA)

100

1000

PV (V)

IN2

I

LOAD

3558 G40

3558 G39

Buck-Boost Regulator Start-Up

Transient, Burst Mode Operation

Buck-Boost Regulator Start-Up

Transient, PWM Mode

PV = 3.6V

IN2

LOAD

PV = 3.6V

IN2

LOAD

R

= 16Ω

R

= 332Ω

V

OUT

1V/DIV

INDUCTOR

CURRENT

I = 200mA/DIV

L

INDUCTOR

CURRENT

I = 200mA/DIV

L

EN2

1V/DIV

EN2

1V/DIV

3558 G42

3558 G41

100μs/DIV

3558f

10

LTC3558

PIN FUNCTIONS

GND (Pin 1): Ground. Connect to Exposed Pad (Pin 21).

V

C2

(Pin 14): Output of the Error Ampliﬁer and Voltage

Compensation Node for the Buck-Boost Regulator. Ex-

ternal Type I or Type III compensation (to FB2) connects

to this pin.

BAT (Pin 2): Charge Current Output. Provides charge cur-

rent to the battery and regulates ﬁnal ﬂoat voltage to 4.2V.

MODE (Pin 3): MODE Pin for Switching Regulators. When

held high, both regulators operate in Burst Mode Opera-

tion. When held low, the buck regulator operates in pulse

skip mode and the buck-boost regulator operates in PWM

mode. This pin is a high impedance input; do not ﬂoat.

EN2 (Pin 15): Enable Input Pin for the Buck-Boost Regu-

lator. This pin is a high impedance input; do not ﬂoat.

Active high.

HPWR (Pin 16): High Current Battery Charging Enabled.

A voltage greater than 1.2V at this pin programs the

BAT pin current at 100% of the maximum programmed

charge current. A voltage less than 0.4V sets the BAT pin

current to 20% of the maximum programmed charge

current. When used with a 1.74k PROG resistor, this pin

can toggle between low power and high power modes per

USB speciﬁcation. A weak pull-down current is internally

applied to this pin to ensure it is low at power-up when

the input is not being driven externally.

FB1 (Pin 4): Buck Regulator Feedback Voltage Pin. Re-

ceives feedback by a resistor divider connected across

the output.

EN1 (Pin 5): Enable Input Pin for the Buck Regulator. This

pin is a high impedance input; do not ﬂoat. Active high.

SW1 (Pin 6): Buck Regulator Switching Node. External

inductor connects to this node.

PV (Pin 7): Input Supply Pin for Buck Regulator. Con-

IN1

NTC (Pin 17): Input to the NTC Thermistor Monitoring

Circuit. The NTC pin connects to a negative temperature

coefﬁcient thermistor which is typically co-packaged with

thebatterypacktodetermineifthebatteryistoohotortoo

cold to charge. If the battery temperature is out of range,

charging is paused until the battery temperature re-enters

the valid range. A low drift bias resistor is required from

nect to BAT and PV . A single 10μF input decoupling

IN2

capacitor to GND is required.

PV (Pin 8): Input Supply Pin for Buck-Boost Regulator.

IN2

Connect to BAT and PV . A single 10μF input decoupling

IN1

capacitor to GND is required.

SWAB2 (Pin 9): Switch Node for Buck-Boost Regulator

ConnectedtotheInternalPowerSwitchesAandB.External

inductor connects between this node and SWCD2.

V

to NTC and a thermistor is required from NTC to

CC

ground. To disable the NTC function, the NTC pin should

be tied to ground.

SWCD2 (Pin 10): Switch Node for Buck-Boost Regulator

ConnectedtotheInternalPowerSwitchesCandD.External

inductor connects between this node and SWAB2.

PROG (Pin 18): Charge Current Program and Charge

Current Monitor Pin. Charge current is programmed by

connecting a resistor from PROG to ground. When charg-

ing in constant-current mode, the PROG pin servos to 1V

if the HPWR pin is pulled high, or 200mV if the HPWR pin

is pulled low. The voltage on this pin always represents

the BAT pin current through the following formula:

V

(Pin 11): Regulated Output Voltage for Buck-Boost

OUT2

Regulator.

SUSP (Pin 12): Suspend Battery Charging Operation. A

voltage greater than 1.2V on this pin puts the battery char-

ger in suspend mode, disables the charger and resets the

termination timer. A weak pull-down current is internally

applied to this pin to ensure it is low at power-up when

the input is not being driven externally.

PROG •800

I_BAT

=

R_PROG

CHRG (Pin 19): Open-Drain Charge Status Output. The

CHRG pin indicates the status of the battery charger. Four

possible states are represented by CHRG charging, not

charging (i.e., the charge current is less than one-tenth

FB2 (Pin 13): Buck-Boost Regulator Feedback Voltage

Pin. Receives feedback by a resistor divider connected

across the output.

3558f

11

LTC3558

PIN FUNCTIONS

of the full-scale charge current), unresponsive battery

(i.e., the battery voltage remains below 2.9V after one half

hour of charging) and battery temperature out of range.

CHRG requires a pull-up resistor and/or LED to provide

indication.

V

(Pin 20): Battery Charger Input. A 1μF decoupling

CC

capacitor to GND is recommended.

Exposed Pad (Pin 21): Ground. The Exposed Pad must

be soldered to PCB ground to provide electrical contact

and rated thermal performance.

BLOCK DIAGRAM

20

V

CC

V

BAT

BODY

CC

1x

800x

MAXER

BAT

2

–

+

CHRG

HPWR

SUSP

19

16

12

T

CA

A

LOGIC

T

DIE

PROG

18

NTCA

NTC REF

NTC

17

3

BATTERY CHARGER

PV

IN1

PV

IN2

MODE

PV

IN1

7

6

EN1

EN2

FB1

5

15

4

UNDERVOLTAGE

LOCKOUT

EN MODE

CLK

MP

MN

–

+

SW1

CONTROL

LOGIC

G

OT

m

DIE

0.8V

T

DIE

TEMPERATURE

BUCK REGULATOR

PV

IN2

V

REF

8

BANDGAP

= 0.8V

V

OUT2

11

BUCK-BOOST REGULATOR

OSCILLATOR

2.25MHz

CLK

EN MODE

A

B

D

C

CLK

–

SWAB2

SWCD2

FB2

9

13

14

CONTROL

LOGIC

V

C2

ERROR

10

AMP

+

0.8V

V

C2

GND

1

EXPOSED PAD

21

3558 BD

3558f

12

LTC3558

OPERATION

The LTC3558 is a linear battery charger with a monolithic

synchronous buck regulator and a monolithic synchro-

nous buck-boost regulator. The buck regulator is inter-

nally compensated and needs no external compensation

components.

For proper operation, the BAT, PV

and PV

pins

IN2

IN1

must be tied together, as shown in Figure 1. Cur-

rent being delivered at the BAT pin is 500mA. Both

switching regulators are enabled. The sum of the

averageinputcurrentsdrawnbybothswitchingregulators

is 200mA. This makes the effective battery charging cur-

rent only 300mA. If the HPWR pin were tied LO, the BAT

pin current would be 100mA. With the switching regulator

conditions unchanged, this would cause the battery to

discharge at 100mA.

Thebatterychargeremploysaconstant-current,constant-

voltage charging algorithm and is capable of charging a

singleLi-Ionbatteryatchargingcurrentsupto950mA.The

usercanprogramthemaximumchargingcurrentavailable

at the BAT pin via a single PROG resistor. The actual BAT

pin current is set by the status of the HPWR pin.

500mA

300mA

USB (5V)

V

BAT

CC

+

SINGLE Li-lon

CELL 3.6V

200mA

PV

IN1

PROG

PV

+

IN2

LTC3558

10μF

R

PROG

SUSP

SWAB2

HIGH

2.2μH

HPWR

EN1

HIGH

SWCD2

OUT2

SW1

HIGH

LOW

EN2

V

MODE

V

OUT1

3558 F01

Figure 1. For Proper Operation, the BAT, PV_IN1and PV_IN2Pins Must Be Tied Together

APPLICATIONS INFORMATION

Battery Charger Introduction

Input Current vs Charge Current

The LTC3558 has a linear battery charger designed to

charge single-cell lithium-ion batteries. The charger uses

a constant-current/constant-voltage charge algorithm

with a charge current programmable up to 950mA. Ad-

ditional features include automatic recharge, an internal

terminationtimer,low-batterytricklechargeconditioning,

bad-battery detection, and a thermistor sensor input for

out of temperature charge pausing.

The battery charger regulates the total current delivered

to the BAT pin; this is the charge current. To calculate the

total input current (i.e., the total current drawn from the

V

pin), it is necessary to sum the battery charge current,

CC

charger quiescent current and PROG pin current.

Undervoltage Lockout (UVLO)

The undervoltage lockout circuit monitors the input volt-

age (V ) and disables the battery charger until V rises

Furthermore, the battery charger is capable of operating

from a USB power source. In this application, charge

current can be programmed to a maximum of 100mA or

500mA per USB power speciﬁcations.

CC

above V

(typically 4V). 200mV of hysteresis prevents

UVLO

oscillations around the trip point. In addition, a differential

undervoltage lockout circuit disables the battery charger

3558f

13

LTC3558

APPLICATIONS INFORMATION

when V falls to within V

(typically 50mV) of the

enters constant-voltage mode, the 4-hour timer is started.

After the safety timer expires, charging of the battery will

discontinue and no more current will be delivered.

CC

DUVLO

BAT voltage.

Suspend Mode

Automatic Recharge

The battery charger can also be disabled by pulling the

SUSP pin above 1.2V. In suspend mode, the battery

drain current is reduced to 1.5μA and the input current is

reduced to 8.5μA.

After the battery charger terminates, it will remain off,

drawing only microamperes of current from the battery.

If the portable product remains in this state long enough,

thebatterywilleventuallyselfdischarge.Toensurethatthe

battery is always topped off, a charge cycle will automati-

Charge Cycle Overview

cally begin when the battery voltage falls below V

RECHRG

When a battery charge cycle begins, the battery charger

ﬁrst determines if the battery is deeply discharged. If the

(typically 4.105V). In the event that the safety timer is

running when the battery voltage falls below V , it

RECHRG

batteryvoltageisbelowV

,typically2.9V,anautomatic

TRKL

will reset back to zero. To prevent brief excursions below

trickle charge feature sets the battery charge current to

V

fromresettingthesafetytimer,thebatteryvoltage

RECHRG

must be below V

10% of the full-scale value.

for more than 1.7ms. The charge

RECHRG

cycle and safety timer will also restart if the V UVLO or

Once the battery voltage is above 2.9V, the battery charger

begins charging in constant-current mode. When the

battery voltage approaches the 4.2V required to maintain

a full charge, otherwise known as the ﬂoat voltage, the

charge current begins to decrease as the battery charger

switches into constant-voltage mode.

CC

DUVLO cycles low and then high (e.g., V is removed

CC

and then replaced) or the charger enters and then exits

suspend mode.

Programming Charge Current

The PROG pin serves both as a charge current program

pin, and as a charge current monitor pin. By design, the

PROG pin current is 1/800th of the battery charge current.

Therefore, connecting a resistor from PROG to ground

programsthechargecurrentwhilemeasuringthePROGpin

voltage allows the user to calculate the charge current.

Trickle Charge and Defective Battery Detection

Any time the battery voltage is below V , the charger

TRKL

goes into trickle charge mode and reduces the charge

current to 10% of the full-scale current. If the battery

voltage remains below V

for more than 1/2 hour, the

TRKL

chargerlatchesthebad-batterystate, automaticallytermi-

nates, and indicates via the CHRG pin that the battery was

unresponsive. If for any reason the battery voltage rises

Full-scale charge current is deﬁned as 100% of the con-

stant-current mode charge current programmed by the

PROG resistor. In constant-current mode, the PROG pin

servosto1VifHPWRishigh,whichcorrespondstocharg-

ing at the full-scale charge current, or 200mV if HPWR

is low, which corresponds to charging at 20% of the full-

scale charge current. Thus, the full-scale charge current

and desired program resistor for a given full-scale charge

current are calculated using the following equations:

above V

, the charger will resume charging. Since the

TRKL

charger has latched the bad-battery state, if the battery

voltagethenfallsbelowV againbutwithoutrisingpast

TRKL

V

ﬁrst, the charger will immediately assume that

RECHRG

the battery is defective. To reset the charger (i.e., when

the dead battery is replaced with a new battery), simply

remove the input voltage and reapply it or put the part in

and out of suspend mode.

800V

R_PROG

I_CHG

=

Charge Termination

800V

I_CHG

R_PROG

=

The battery charger has a built-in safety timer that sets

the total charge time for 4 hours. Once the battery voltage

rises above V

(typically 4.105V) and the charger

RECHRG

3558f

14

LTC3558

APPLICATIONS INFORMATION

In any mode, the actual battery current can be determined

by monitoring the PROG pin voltage and using the follow-

ing equation:

charge current has dropped to below 10% of the full-scale

current, the CHRG pin is released (high impedance). If

a fault occurs after the CHRG pin is released, the pin re-

mains high impedance. However, if a fault occurs before

the CHRG pin is released, the pin is switched at 35kHz.

Whileswitching,itsdutycycleismodulatedbetweenahigh

and low value at a very low frequency. The low and high

duty cycles are disparate enough to make an LED appear

to be on or off thus giving the appearance of “blinking”.

Each of the two faults has its own unique “blink” rate for

human recognition as well as two unique duty cycles for

microprocessor recognition.

PROG

R_PROG

I_BAT

=

•800

Thermal Regulation

To prevent thermal damage to the IC or surrounding

components, an internal thermal feedback loop will auto-

matically decrease the programmed charge current if the

die temperature rises to approximately 115°C. Thermal

regulation protects the battery charger from excessive

temperature due to high power operation or high ambient

thermal conditions and allows the user to push the limits

of the power handling capability with a given circuit board

design without risk of damaging the LTC3558 or external

components. The beneﬁt of the LTC3558 battery charger

thermal regulation loop is that charge current can be set

according to actual conditions rather than worst-case

conditions with the assurance that the battery charger

will automatically reduce the current in worst-case con-

ditions.

Table 1 illustrates the four possible states of the CHRG

pin when the battery charger is active.

Table 1. CHRG Output Pin

MODULATION

(BLINK)

STATUS

FREQUENCY

0Hz

FREQUENCY

DUTY CYCLE

100%

Charging

0 Hz (Lo-Z)

I

< C/10

0Hz

0 Hz (Hi-Z)

0%

BAT

35kHz

1.5Hz at 50%

6.1Hz at 50%

6.25%, 93.75%

12.5%, 87.5%

NTC Fault

Bad Battery

An NTC fault is represented by a 35kHz pulse train whose

duty cycle alternates between 6.25% and 93.75% at a

1.5Hz rate. A human will easily recognize the 1.5Hz rate as

a “slow” blinking which indicates the out of range battery

temperaturewhileamicroprocessorwillbeabletodecode

either the 6.25% or 93.75% duty cycles as an NTC fault.

Charge Status Indication

The CHRG pin indicates the status of the battery charger.

Four possible states are represented by CHRG charging,

notcharging,unresponsivebatteryandbatterytemperature

out of range.

If a battery is found to be unresponsive to charging (i.e.,

ThesignalattheCHRGpincanbeeasilyrecognizedasone

of the above four states by either a human or a micropro-

cessor. The CHRG pin, which is an open-drain output, can

drive an indicator LED through a current limiting resistor

for human interfacing, or simply a pull-up resistor for

microprocessor interfacing.

its voltage remains below V

for over 1/2 hour), the

TRKL

CHRG pin gives the battery fault indication. For this fault,

a human would easily recognize the frantic 6.1Hz “fast”

blinking of the LED while a microprocessor would be able

to decode either the 12.5% or 87.5% duty cycles as a bad

battery fault.

To make the CHRG pin easily recognized by both humans

and microprocessors, the pin is either a low for charging,

a high for not charging, or it is switched at high frequency

(35kHz) to indicate the two possible faults: unresponsive

battery and battery temperature out of range.

Although very improbable, it is possible that a duty cycle

reading could be taken at the bright-dim transition (low

duty cycle to high duty cycle). When this happens the

duty cycle reading will be precisely 50%. If the duty cycle

reading is 50%, system software should disqualify it and

take a new duty cycle reading.

When charging begins, CHRG is pulled low and remains

low for the duration of a normal charge cycle. When the

3558f

15

LTC3558

APPLICATIONS INFORMATION

NTC Thermistor

value of R25 or approximately 54k (for a Vishay “Curve

1” thermistor, this corresponds to approximately 40°C). If

thebatterychargerisinconstant-voltagemode, thesafety

timer will pause until the thermistor indicates a return to

a valid temperature.

The battery temperature is measured by placing a nega-

tive temperature coefﬁcient (NTC) thermistor close to the

battery pack. The NTC circuitry is shown in Figure 3.

To use this feature, connect the NTC thermistor, R

,

NTC

NOM

As the temperature drops, the resistance of the NTC

thermistor rises. The battery charger is also designed

to pause charging when the value of the NTC thermistor

increases to 3.25 times the value of R25. For a Vishay

“Curve 1” thermistor, this resistance, 325k, corresponds

to approximately 0°C. The hot and cold comparators each

haveapproximately3°Cofhysteresistopreventoscillation

about the trip point. Grounding the NTC pin disables all

NTC functionality.

betweentheNTCpinandground,andabiasresistor,R

from V to NTC. R

should be a 1% resistor with a

CC

NOM

value equal to the value of the chosen NTC thermistor at

25°C (R25). A 100k thermistor is recommended since

thermistor current is not measured by the battery charger

and its current will have to be considered for compliance

with USB speciﬁcations.

The battery charger will pause charging when the re-

sistance of the NTC thermistor drops to 0.54 times the

DUVLO, UVLO AND SUSPEND

IF SUSP < 0.4V AND

DISABLE MODE

NO

POWER

CHRG HIGH IMPEDANCE

ON

V

CC

V

CC

> 4V AND

> BAT + 130mV?

YES

FAULT

NTC FAULT

STANDBY MODE

BATTERY CHARGING SUSPENDED

NO CHARGE CURRENT

CHRG PULSES

CHRG HIGH IMPEDANCE

NO FAULT

BAT b 2.9V

2.9V < BAT < 4.105V

BAT > 2.9V

TRICKLE CHARGE MODE

CONSTANT CURRENT MODE

4-HOUR

TIMEOUT

1/10 FULL CHARGE CURRENT

CHRG STRONG PULL-DOWN

30 MINUTE TIMER BEGINS

FULL CHARGE CURRENT

CHRG STRONG PULL-DOWN

30 MINUTE

TIMEOUT

DEFECTIVE BATTERY

CONSTANT VOLTAGE MODE

NO CHARGE CURRENT

CHRG PULSES

4-HOUR TERMINATION TIMER

BEGINS

BAT DROPS BELOW 4.105V

4-HOUR TERMINATION TIMER RESETS

3558 F02

Figure 2. State Diagram of Battery Charger Operation

3558f

16

LTC3558

APPLICATIONS INFORMATION

Alternate NTC Thermistors and Biasing

Therefore, the hot trip point is set when:

The battery charger provides temperature qualiﬁed

charging if a grounded thermistor and a bias resistor are

connected to the NTC pin. By using a bias resistor whose

value is equal to the room temperature resistance of the

thermistor (R25) the upper and lower temperatures are

pre-programmed to approximately 40°C and 0°C, respec-

tively (assuming a Vishay “Curve 1” thermistor).

R_NTC|HOT

• V_CC= 0.349 • V_CC

R_NOM+ R_NTC|HOT

and the cold trip point is set when:

R_NTC|COLD

• V_CC= 0.765 • V_CC

R_NOM+ R_NTC|COLD

The upper and lower temperature thresholds can be ad-

justed by either a modiﬁcation of the bias resistor value

or by adding a second adjustment resistor to the circuit.

If only the bias resistor is adjusted, then either the upper

or the lower threshold can be modiﬁed but not both. The

other trip point will be determined by the characteristics

of the thermistor. Using the bias resistor in addition to an

adjustmentresistor,boththeupperandthelowertempera-

ture trip points can be independently programmed with

the constraint that the difference between the upper and

lower temperature thresholds cannot decrease. Examples

of each technique are given below.

Solving these equations for R

results in the following:

and R

NTC|HOT

NTC|COLD

R

= 0.536 • R

NTC|HOT

NOM

and

R

= 3.25 • R

NTC|COLD

NOM

By setting R

equal to R25, the above equations result

NOM

= 0.536 and r

in r

= 3.25. Referencing these ratios

HOT

COLD

to the Vishay Resistance-Temperature Curve 1 chart gives

a hot trip point of about 40°C and a cold trip point of about

0°C. The difference between the hot and cold trip points

is approximately 40°C.

NTC thermistors have temperature characteristics which

areindicatedonresistance-temperatureconversiontables.

TheVishay-DalethermistorNTHS0603N011-N1003F,used

in the following examples, has a nominal value of 100k

and follows the Vishay “Curve 1” resistance-temperature

characteristic.

By using a bias resistor, R

, different in value from

NOM

R25, the hot and cold trip points can be moved in either

direction.Thetemperaturespanwillchangesomewhatdue

to the nonlinear behavior of the thermistor. The following

equations can be used to easily calculate a new value for

the bias resistor:

In the explanation below, the following notation is used.

R25 = Value of the thermistor at 25°C

r_HOT

0.536

R_NOM

=

•R25

R

= Value of thermistor at the cold trip point

NTC|COLD

= Value of the thermistor at the hot trip point

NTC|HOT

r_COLD

3.25

and r

R_NOM

=

•R25

r

= Ratio of R

to R25

COLD

NTC|COLD

where r

are the resistance ratios at the de-

COLD

= Ratio of R

to R25

HOT

NTC|HOT

sired hot and cold trip points. Note that these equations

are linked. Therefore, only one of the two trip points can

be chosen, the other is determined by the default ratios

designed in the IC. Consider an example where a 60°C

hot trip point is desired.

R

= Primary thermistor bias resistor (see Figure 3)

NOM

R1 = Optional temperature range adjustment resistor (see

Figure 4)

The trip points for the battery charger’s temperature quali-

FromtheVishayCurve1R-Tcharacteristics,r is0.2488

ﬁcation are internally programmed at 0.349 • V for the

HOT

should be set

CC

at 60°C. Using the above equation, R

hot threshold and 0.765 • V for the cold threshold.

NOM

CC

3558f

17

LTC3558

APPLICATIONS INFORMATION

to 46.4k. With this value of R

, the cold trip point is

For example, to set the trip points to 0°C and 45°C with

a Vishay Curve 1 thermistor choose:

NOM

about 16°C. Notice that the span is now 44°C rather than

the previous 40°C.

3.266 – 0.4368

R_NOM

=

•100k = 104.2k

The upper and lower temperature trip points can be inde-

pendentlyprogrammedbyusinganadditionalbiasresistor

as shown in Figure 4. The following formulas can be used

2.714

the nearest 1% value is 105k.

to compute the values of R

and R1:

NOM

R1 = 0.536 • 105k – 0.4368 • 100k = 12.6k

r_COLD–r_HOT

the nearest 1% value is 12.7k. The ﬁnal solution is shown

in Figure 4 and results in an upper trip point of 45°C and

a lower trip point of 0°C.

R_NOM

=

•R25

2.714

R1= 0.536 •R_NOM–r_HOT•R25

NTC BLOCK

V

CC

20

17

0.765 • V

CC

0.765 • V

CC

(NTC RISING)

R

–

+

–

+

R

NOM

105k

100k

TOO_COLD

TOO_HOT

TOO_COLD

TOO_HOT

NTC

17

R1

12.7k

R

100k

NTC

–

+

–

+

R

100k

NTC

0.349 • V

CC

(NTC FALLING)

CC

(NTC FALLING)

+

–

+

–

NTC_ENABLE

0.017 • V

CC

(NTC FALLING)

0.017 • V

CC

(NTC FALLING)

3558 F04

3558 F03

Figure 4. NTC Thermistor Circuit with Additional Bias Resistor

Figure 3. Typical NTC Thermistor Circuit

3558f

18

LTC3558

APPLICATIONS INFORMATION

USB and Wall Adapter Power

current. It is not necessary to perform any worst-case

power dissipation scenarios because the LTC3558 will

automatically reduce the charge current to maintain the

die temperature at approximately 105°C. However, the

approximate ambient temperature at which the thermal

feedback begins to protect the IC is:

Although the battery charger is designed to draw power

from a USB port to charge Li-Ion batteries, a wall adapter

can also be used. Figure 5 shows an example of how to

combine wall adapter and USB power inputs. A P-channel

MOSFET, MP1, is used to prevent back conduction into

the USB port when a wall adapter is present and Schottky

diode, D1, is used to prevent USB power loss through the

1k pull-down resistor.

T_A= 105°C–P_Dθ_JA

T = 105°C– V – V

•I_BAT•θ_JA

(

)

A

CC

BAT

Example: Consider an LTC3558 operating from a USB port

providing 500mA to a 3.5V Li-Ion battery. The ambient

temperatureabovewhichtheLTC3558willbegintoreduce

the 500mA charge current is approximately:

Typically, a wall adapter can supply signiﬁcantly more

current than the 500mA-limited USB port. Therefore, an

N-channelMOSFET,MN1,andanextraprogramresistorare

used to increase the maximum charge current to 950mA

when the wall adapter is present.

T = 105°C – 5V – 3.5V • 500mA •68°C / W

(

) (

)

A

T_A= 105°C – 0.75W •68°C / W = 105°C – 51°C

T_A= 54°C

5V WALL

I

BAT

ADAPTER

BAT

BATTERY

CHARGER

V

CC

950mA I

CHG

D1

The LTC3558 can be used above 70°C, but the charge cur-

rentwillbereducedfrom500mA. Theapproximatecurrent

at a given ambient temperature can be calculated:

USB

POWER

MP1

500mA I

+

CHG

Li-Ion

BATTERY

PROG

1.65k

105°C– T_A

MN1

1.74k

I_BAT

=

1k

V – V

•θ

(

)

CC

BAT

JA

3558 F05

Using the previous example with an ambient tem-

perature of 88°C, the charge current will be reduced to

approximately:

Figure 5. Combining Wall Adapter and USB Power

105°C – 88°C

17°C

I_BAT

=

Power Dissipation

5V – 3.5V •68°C / W 102°C / A

(

)

I_BAT= 167mA

The conditions that cause the LTC3558 to reduce charge

current through thermal feedback can be approximated

by considering the power dissipated in the IC. For high

charge currents, the LTC3558 power dissipation is

approximately:

Furthermore, the voltage at the PROG pin will change

proportionally with the charge current as discussed in

the Programming Charge Current section.

It is important to remember that LTC3558 applications do

notneedtobedesignedforworst-casethermalconditions

since the IC will automatically reduce power dissipation

when the junction temperature reaches approximately

105°C.

P = V – V

•I

BAT

(

)

D

CC

BAT

where P is the power dissipated, V is the input supply

D

CC

voltage, V is the battery voltage, and I is the charge

BAT

3558f

19

LTC3558

APPLICATIONS INFORMATION

Battery Charger Stability Considerations

Average,ratherthaninstantaneous,batterycurrentmaybe

of interest to the user. For example, if a switching power

supply operating in low-current mode is connected in

parallel with the battery, the average current being pulled

out of the BAT pin is typically of more interest than the

instantaneous current pulses. In such a case, a simple RC

ﬁltercanbeusedonthePROGpintomeasuretheaverage

battery current as shown in Figure 6. A 10k resistor has

been added between the PROG pin and the ﬁlter capacitor

to ensure stability.

TheLTC3558batterychargercontainstwocontrolloops:the

constant-voltageandconstant-currentloops.Theconstant-

voltage loop is stable without any compensation when a

battery is connected with low impedance leads. Excessive

lead length, however, may add enough series inductance

to require a bypass capacitor of at least 1.5μF from BAT

to GND. Furthermore, a 4.7μF capacitor with a 0.2Ω to 1Ω

series resistor from BAT to GND is required to keep ripple

voltage low when the battery is disconnected.

USB Inrush Limiting

High value capacitors with very low ESR (especially

ceramic) reduce the constant-voltage loop phase margin,

possibly resulting in instability. Ceramic capacitors up to

22μF may be used in parallel with a battery, but larger

ceramics should be decoupled with 0.2Ω to 1Ω of series

resistance.

When a USB cable is plugged into a portable product,

the inductance of the cable and the high-Q ceramic input

capacitorformanL-Cresonantcircuit.Ifthereisnotmuch

impedance in the cable, it is possible for the voltage at

the input of the product to reach as high as twice the

USB voltage (~10V) before it settles out. In fact, due to

the high voltage coefﬁcient of many ceramic capacitors

(a nonlinearity), the voltage may even exceed twice the

USB voltage. To prevent excessive voltage from damag-

ing the LTC3558 during a hot insertion, the soft connect

circuit in Figure 7 can be employed.

In constant-current mode, the PROG pin is in the feedback

loop,notthebattery.Becauseoftheadditionalpolecreated

bythePROGpincapacitance,capacitanceonthispinmust

be kept to a minimum. With no additional capacitance on

the PROG pin, the charger is stable with program resistor

values as high as 25K. However, additional capacitance on

this node reduces the maximum allowed program resis-

tor. The pole frequency at the PROG pin should be kept

above 100kHz. Therefore, if the PROG pin is loaded with a

In the circuit of Figure 7, capacitor C1 holds MP1 off

when the cable is ﬁrst connected. Eventually C1 begins

to charge up to the USB input voltage applying increasing

gate support to MP1. The long time constant of R1 and

C1 prevents the current from building up in the cable too

fast thus dampening out any resonant overshoot.

capacitance,C

,thefollowingequationshouldbeused

PROG

to calculate the maximum resistance value for R

:

PROG

1

R_PROG

≤

2π •10⁵•C_PROG

MP1

Si2333

V

CC

C1

100nF

LTC3558

5V USB

INPUT

CHARGE

10k

C2

10μF

LTC3558

USB CABLE

CURRENT

MONITOR

CIRCUITRY

PROG

R1

40k

GND

R

C

FILTER

PROG

GND

3558 F06

3558 F07

Figure 6. Isolated Capacitive Load on PROG Pin and Filtering

Figure 7. USB Soft Connect Circuit

3558f

20

LTC3558

APPLICATIONS INFORMATION

Buck Switching Regulator General Information

Buck Switching Regulator

Output Voltage Programming

The LTC3558 contains a 2.25MHz constant-frequency

current mode buck switching regulator that can provide

up to 400mA. The switcher can be programmed for a

minimumoutputvoltageof0.8Vandcanbeusedtopower

a microcontroller core, microcontroller I/O, memory or

other logic circuitry. The regulator supports 100% duty

cycle operation (dropout mode) when the input voltage

drops very close to the output voltage and is also capable

of operating in Burst Mode operation for highest efﬁcien-

ciesatlightloads(BurstModeoperationispinselectable).

The buck switching regulator also includes soft-start to

limit inrush current when powering on, short-circuit cur-

rent protection, and switch node slew limiting circuitry to

reduce radiated EMI.

The buck switching regulator can be programmed for

output voltages greater than 0.8V. The output voltage

for the buck switching regulator is programmed using a

resistor divider from the switching regulator output con-

nected to its feedback pin (FB1), as shown in Figure 8,

such that:

V

= 0.8(1 + R1/R2)

OUT

Typical values for R1 are in the range of 40k to 1M. The

capacitor C_FBcancels the pole created by feedback re-

sistors and the input capacitance of the FB pin and also

helps to improve transient response for output voltages

much greater than 0.8V. A variety of capacitor sizes can

be used for C_FBbut a value of 10pF is recommended for

most applications. Experimentation with capacitor sizes

between 2pF and 22pF may yield improved transient

response if so desired by the user.

A MODE pin sets the buck switching regulator in Burst

Modeoperationorpulseskipoperatingmode. Theregula-

tor is enabled individually through its enable pin. The buck

regulator input supply (PV ) should be connected to the

IN1

Buck Switching Regulator Operating Modes

battery pin (BAT) and PV . This allows the undervoltage

IN2

lockoutcircuitontheBATpintodisablethebuckregulators

when the BAT voltage drops below 2.45V. Do not drive the

buck switching regulator from a voltage other than BAT.

The buck switching regulator includes two possible oper-

ating modes to meet the noise/power needs of a variety

of applications.

A 10μF decoupling capacitor from the PV pin to GND

IN1

In pulse skip mode, an internal latch is set at the start of

every cycle, which turns on the main P-channel MOSFET

is recommended.

P

VIN

EN

MP

SW

PWM

CONTROL

L

V

OUT

C

O

C

FB

MODE

MN

R1

R2

FB

0.8V

GND

3558 F08

Figure 8. Buck Converter Application Circuit

3558f

21

LTC3558

APPLICATIONS INFORMATION

switch.Duringeachcycle,acurrentcomparatorcompares

thepeakinductorcurrenttotheoutputofanerrorampliﬁer.

The output of the current comparator resets the internal

latch,whichcausesthemainP-channelMOSFETswitchto

turn off and the N-channel MOSFET synchronous rectiﬁer

to turn on. The N-channel MOSFET synchronous rectiﬁer

turns off at the end of the 2.25MHz cycle or if the current

through the N-channel MOSFET synchronous rectiﬁer

drops to zero. Using this method of operation, the error

ampliﬁer adjusts the peak inductor current to deliver the

required output power. All necessary compensation is

internal to the buck switching regulator requiring only a

single ceramic output capacitor for stability. At light loads

in pulse skip mode, the inductor current may reach zero

on each pulse which will turn off the N-channel MOSFET

synchronous rectiﬁer. In this case, the switch node (SW1)

goes high impedance and the switch node voltage will

“ring”. This is discontinuous operation, and is normal be-

haviorforaswitchingregulator. Atverylightloadsinpulse

skipmode, thebuckswitchingregulatorwillautomatically

skip pulses as needed to maintain output regulation. At

powered down, helping conserve battery power. When

the output voltage drops below a pre-determined value,

the buck switching regulator circuitry is powered on and

anotherburstcyclebegins.Thesleeptimedecreasesasthe

loadcurrentincreases.Beyondacertainloadcurrentpoint

(about 1/4 rated output load current) the buck switching

regulator will switch to a low noise constant-frequency

PWM mode of operation, much the same as pulse skip

operation at high loads. For applications that can tolerate

some output ripple at low output currents, Burst Mode

operation provides better efﬁciency than pulse skip at

light loads.

The buck switching regulator allows mode transition on-

the-ﬂy,providingseamlesstransitionbetweenmodeseven

under load. This allows the user to switch back and forth

between modes to reduce output ripple or increase low

current efﬁciency as needed. Burst Mode operation is set

by driving the MODE pin high, while pulse skip mode is

achieved by driving the MODE pin low.

Buck Switching Regulator in Shutdown

high duty cycle (V

> PV /2) in pulse skip mode, it is

OUT

IN1

The buck switching regulator is in shutdown when not

enabledforoperation.Inshutdown,allcircuitryinthebuck

switchingregulatorisdisconnectedfromtheregulatorinput

supply, leaving only a few nanoamps of leakage pulled to

ground through a 13k resistor on the switch (SW1) pin

when in shutdown.

possible for the inductor current to reverse causing the

buck converter to switch continuously. Regulation and

low noise operation are maintained but the input supply

current will increase to a couple mA due to the continuous

gate switching.

During Burst Mode operation, the buck switching regula-

tor automatically switches between ﬁxed frequency PWM

operation and hysteretic control as a function of the load

current.Atlightloadsthebuckswitchingregulatorcontrols

the inductor current directly and use a hysteretic control

loop to minimize both noise and switching losses. During

Burst Mode operation, the output capacitor is charged to a

voltage slightly higher than the regulation point. The buck

switching regulator then goes into sleep mode, during

which the output capacitor provides the load current. In

sleep mode, most of the switching regulator’s circuitry is

Buck Switching Regulator Dropout Operation

It is possible for the buck switching regulator’s input volt-

age to approach its programmed output voltage (e.g., a

battery voltage of 3.4V with a programmed output voltage

of 3.3V). When this happens, the PMOS switch duty cycle

increasesuntilitisturnedoncontinuouslyat100%.Inthis

dropoutcondition,therespectiveoutputvoltageequalsthe

regulator’s input voltage minus the voltage drops across

the internal P-channel MOSFET and the inductor.

3558f

22

LTC3558

APPLICATIONS INFORMATION

Buck Switching Regulator Soft-Start Operation

Buck Switching Regulator Inductor Selection

Soft-startisaccomplishedbygraduallyincreasingthepeak

inductorcurrentforeachswitchingregulatorovera500μs

period. This allows an output to rise slowly, helping mini-

mize the battery in-rush current required to charge up the

regulator’soutputcapacitor.Asoft-startcycleoccurswhen

the buck switcher ﬁrst turns on, or after a fault condition

has occurred (thermal shutdown or UVLO). A soft-start

cycle is not triggered by changing operating modes using

theMODEpin.Thisallowsseamlessoutputoperationwhen

transitioning between operating modes.

The buck switching regulator is designed to work with

inductors in the range of 2.2μH to 10μH, but for most

applications a 4.7μH inductor is suggested. Larger value

inductors reduce ripple current which improves output

ripple voltage. Lower value inductors result in higher

ripple current which improves transient response time.

To maximize efﬁciency, choose an inductor with a low DC

resistance.Fora1.2Voutputefﬁciencyisreducedabout2%

forevery100mΩseriesresistanceat400mAloadcurrent,

andabout2%forevery300mΩseriesresistanceat100mA

load current. Choose an inductor with a DC current rating

at least 1.5 times larger than the maximum load current to

ensure that the inductor does not saturate during normal

operation. If output short-circuit is a possible condition

the inductor should be rated to handle the maximum peak

current speciﬁed for the buck regulators.

Buck Switching Regulator

Switching Slew Rate Control

The buck switching regulator contains circuitry to limit

the slew rate of the switch node (SW1). This circuitry is

designed to transition the switch node over a period of a

couple of nanoseconds, signiﬁcantly reducing radiated

EMI and conducted supply noise while maintaining high

efﬁciency.

Differentcorematerialsandshapeswillchangethesize/cur-

rentandprice/currentrelationshipofaninductor.Toroidor

shieldedpotcoresinferriteorpermalloymaterialsaresmall

and don’t radiate much energy, but generally cost more

than powdered iron core inductors with similar electrical

characteristics. Inductors that are very thin or have a very

small volume typically have much higher DCR losses, and

will not give the best efﬁciency. The choice of which style

inductor to use often depends more on the price vs size,

performance, and any radiated EMI requirements than on

what the buck regulator requires to operate.

Buck Switching Regulator Low Supply Operation

An undervoltage lockout (UVLO) circuit on PV shuts

IN1

downthestep-downswitchingregulatorswhenBATdrops

below2.45V.ThisUVLOpreventsthebuckswitchingregu-

lator from operating at low supply voltages where loss of

regulation or other undesirable operation may occur.

The inductor value also has an effect on Burst Mode

operation. Lower inductor values will cause Burst Mode

switching frequency to increase.

3558f

23

LTC3558

APPLICATIONS INFORMATION

Table 2 shows several inductors that work well with the

LTC3558 buck switching regulator. These inductors offer

a good compromise in current rating, DCR and physical

size. Consult each manufacturer for detailed information

on their entire selection of inductors.

for most applications. For good transient response and

stability the output capacitor should retain at least 4μF

of capacitance over operating temperature and bias volt-

age.Thebuckswitchingregulatorinputsupplyshouldbe

bypassed with a 10μF capacitor. Consult manufacturer

for detailed information on their selection and speciﬁca-

tions of ceramic capacitors. Many manufacturers now

offer very thin (< 1mm tall) ceramic capacitors ideal for

use in height-restricted designs. Table 3 shows a list of

several ceramic capacitor manufacturers.

Buck Switching Regulator

Input/Output Capacitor Selection

LowESR(equivalentseriesresistance)ceramiccapacitors

should be used at switching regulator outputs as well as

the switching regulator input supply. Ceramic capacitor

dielectrics are a compromise between high dielectric

constant and stability versus temperature and versus

DC bias voltage. The X5R/X7R dielectrics offer the best

compromisewithhighdielectricconstantandacceptable

performance over temperature and under bias. Do not

use Y5V dielectrics. A 10μF output capacitor is sufﬁcient

Table 3: Recommended Ceramic Capacitor Manufacturers

AVX

Murata

(803) 448-9411

(714) 852-2001

(408) 537-4150

(888) 835-6646

www.avxcorp.com

www.murata.com

www.t-yuden.com

www.tdk.com

Taiyo Yuden

TDK

Table 2. Recommended Inductors for Buck Switching Regulators

L

(μH)

MAX I

(A)

MAX DCR

(mΩ)

SIZE IN mm

(L × W × H)

DC

INDUCTOR TYPE

MANUFACTURER

DE2818C

DE2812C

4.7

1.25

1.15

72*

130*

Toko

www.toko.com

3 × 2.8 × 1.8

3 × 2.8 × 1.2

CDRH3D16

4.7

0.9

110

Sumida

www.sumida.com

4 × 4 × 1.8

SD3118

SD3112

4.7

1.3

0.8

162

246

Cooper

www.cooperet.com

3.1 × 3.1 × 1.8

3.1 × 3.1 × 1.2

LPS3015

4.7

1.1

200

Coilcraft

www.coilcraft.com

3 × 3 × 1.5

*Typical DCR

3558f

24

LTC3558

APPLICATIONS INFORMATION

Buck-Boost Switching Regulator

the converter will operate in four-switch mode. While

operating in four-switch mode, switches turn on as per

the following sequence: switches A and D → switches A

and C → switches B and D → switches A and D.

The LTC3558 contains a 2.25MHz constant-frequency,

voltage mode, buck-boost switching regulator. The regu-

lator provides up to 400mA of output load current. The

buck-boost switching regulator can be programmed for a

minimumoutputvoltageof2.75Vandcanbeusedtopower

a microcontroller core, microcontroller I/O, memory, disk

drive, or other logic circuitry. To suit a variety of applica-

tions, different mode functions allow the user to trade off

noise for efﬁciency. Two modes are available to control the

operationofthebuck-boostregulator.Atmoderatetoheavy

loads, the constant-frequency PWM mode provides the

leastnoiseswitchingsolution.Atlighterloads,BurstMode

operationmaybeselected. Regulationismaintainedbyan

error ampliﬁer that compares the divided output voltage

with a reference and adjusts the compensation voltage

accordinglyuntiltheFB2voltagehasstabilizedat0.8V.The

buck-boost switching regulator also includes soft-start to

limit inrush current and voltage overshoot when powering

on, short-circuit current protection, and switch node slew

limiting circuitry for reduced radiated EMI.

Buck-Boost Regulator Burst Mode Operation

In Burst Mode operation, the switching regulator uses a

hystereticfeedbackvoltagealgorithmtocontroltheoutput

voltage. By limiting FET switching and using a hysteretic

control loop switching losses are greatly reduced. In

this mode, output current is limited to 50mA. While in

Burst Mode operation, the output capacitor is charged

to a voltage slightly higher than the regulation point. The

buck-boost converter then goes into a SLEEP state, dur-

ing which the output capacitor provides the load current.

The output capacitor is charged by charging the inductor

until the input current reaches 250mA typical, and then

discharging the inductor until the reverse current reaches

0mA typical. This process of bursting current is repeated

until the feedback voltage has charged to the reference

voltage plus 6mV (806mV typical). In the SLEEP state,

most of the regulator’s circuitry is powered down, helping

to conserve battery power. When the feedback voltage

drops below the reference voltage minus 6mV (794mV

typical), the switching regulator circuitry is powered on

and another burst cycle begins. The duration for which the

regulator operates in SLEEP depends on the load current

and output capacitor value. The SLEEP time decreases

as the load current increases. The maximum deliverable

load current in Burst Mode operation is 50mA typical.

The buck-boost regulator may not enter SLEEP if the load

current is greater than 50mA. If the load current increases

beyond this point while in Burst Mode operation, the out-

put may lose regulation. Burst Mode operation provides a

signiﬁcant improvement in efﬁciency at light loads at the

expense of higher output ripple when compared to PWM

mode. For many noise-sensitive systems, Burst Mode

operation might be undesirable at certain times (i.e., dur-

ing a transmit or receive cycle of a wireless device), but

highly desirable at others (i.e., when the device is in low

power standby mode).

Buck-Boost Regulator PWM Operating Mode

In PWM mode, the voltage seen at the feedback node is

compared to a 0.8V reference. From the feedback voltage,

an error ampliﬁer generates an error signal seen at the

V

C2

pin. This error signal controls PWM waveforms that

modulate switches A (input PMOS), B (input NMOS), C

(output NMOS), and D (output PMOS). Switches A and

B operate synchronously, as do switches C and D. If the

input voltage is signiﬁcantly greater than the programmed

output voltage, then the regulator will operate in buck

mode. In this case, switches A and B will be modulated,

withswitchDalwayson(andswitchCalwaysoff), tostep-

down the input voltage to the programmed output. If the

input voltage is signiﬁcantly less than the programmed

output voltage, then the converter will operate in boost

mode. In this case, switches C and D are modulated, with

switch A always on (and switch B always off), to step up

the input voltage to the programmed output. If the input

voltage is close to the programmed output voltage, then

3558f

25

LTC3558

APPLICATIONS INFORMATION

Buck-Boost Switching Regulator Output Voltage

Programming

The output ﬁlter zero is given by:

1

f_{FILTER_ZERO}

=

Hz

The buck-boost switching regulator can be programmed

foroutputvoltagesgreaterthan2.75Vandlessthan5.45V.

To program the output voltage, a resistor divider is con-

2• π •R_ESR•C_OUT

where R

is the capacitor equivalent series resistance.

ESR

nected between V

and the feedback node (FB2) as

OUT2

A troublesome feature in boost mode is the right-half

plane zero (RHP), and is given by:

shown in Figure 9. The output voltage is given by V

= 0.8(1 + R1/R2).

OUT2

2

PV

IN2

f_RHPZ

=

Hz

LTC3558

2• π •I_OUT•L • V_OUT2

V

OUT2

R1

R2

The loop gain is typically rolled off before the RHP zero

frequency.

FB2

AsimpleTypeIcompensationnetwork,asshowninFigure

10, can be incorporated to stabilize the loop, but at the

costofreducedbandwidthandslowertransientresponse.

To ensure proper phase margin, the loop requires to be

crossed over a decade before the LC double pole.

3558 F09

Figure 9. Programming the Buck-Boost Output Voltage Requires

a Resistor Divider Connected Between V_OUT2and FB2

The unity-gain frequency of the error ampliﬁer with the

Type I compensation is given by:

Closing the Feedback Loop

TheLTC3558incorporatesvoltagemodePWMcontrol.The

control to output gain varies with operation region (buck,

boost, buck-boost), but is usually no greater than 20. The

output ﬁlter exhibits a double pole response given by:

1

f_UG

=

Hz

2• π •R1•C_P1

1

f_{FILTER_POLE}

=

Hz

2• π • L •C_OUT

where C

is the output ﬁlter capacitor.

OUT

V

OUT2

R1

0.8V

FB2

+

–

ERROR

AMP

C

R2

P1

V

C2

3558 F10

Figure 10. Error Ampliﬁer with Type I Compensation

3558f

26

LTC3558

APPLICATIONS INFORMATION

Mostapplicationsdemandanimprovedtransientresponse

toallowasmalleroutputﬁltercapacitor.Toachieveahigher

bandwidth, Type III compensation is required. Two zeros

are required to compensate for the double-pole response.

at the ﬁlter double pole. If they are placed at too low of a

frequency, theywillintroducetoomuchgaintothesystem

and the crossover frequency will be too high. The two high

frequency poles should be placed such that the system

crosses unity gain during the phase bump introduced

by the zeros and before the boost right-half plane zero

and such that the compensator bandwidth is less than

the bandwidth of the error amp (typically 900kHz). If the

gain of the compensation network is ever greater than

the gain of the error ampliﬁer, then the error ampliﬁer no

longer acts as an ideal op amp, and another pole will be

introduced at the same point.

Type III compensation also reduces any V

overshoot

OUT2

seen during a start-up condition. A Type III compensa-

tion circuit is shown in Figure 11 and yields the following

transfer function:

V_C2

1

=

V_OUT2R1(C1+ C2)

(1+ sR2C2)[1+ s(R1+ R3)C3]

•

s 1+ sR2(C1||C2) (1+ sR3C3)

⎡

⎤

⎣

⎦

Recommended Type III compensation components for a

3.3V output are:

A Type III compensation network attempts to introduce

a phase bump at a higher frequency than the LC double

pole. This allows the system to cross unity gain after the

LC double pole, and achieve a higher bandwidth. While

attempting to cross over after the LC double pole, the

system must still cross over before the boost right-half

plane zero. If unity gain is not reached sufﬁciently before

the right-half plane zero, then the –180° of phase lag from

the LC double pole combined with the –90° of phase lag

from the right-half plane zero will result in negating the

phase bump of the compensator.

R1: 324kΩ

R : 105kΩ

FB

C1: 10pF

R2: 15kΩ

C2: 330pF

R3: 121kΩ

C3: 33pF

C

L

: 22ꢀF

OUT

The compensator zeros should be placed either before

or only slightly after the LC double pole such that their

positive phase contributions offset the –180° that occurs

: 2.2ꢀH

OUT

V

OUT2

R3

C3

0.8V

+

R1

ERROR

AMP

FB2

–

R

C2

FB

V

C2

R2

C1

3558 F11

Figure 11. Error Ampliﬁer with Type III Compensation

3558f

27

LTC3558

APPLICATIONS INFORMATION

Input Current Limit

Buck-Boost Switching Regulator Inductor Selection

The buck-boost switching regulator is designed to work

with inductors in the range of 1μH to 5μH. For most

applications, a 2.2μH inductor will sufﬁce. Larger value

inductors reduce ripple current which improves output

ripple voltage. Lower value inductors result in higher

ripple current and improved transient response time.

To maximize efﬁciency, choose an inductor with a low

DC resistance and a DC current rating at least 1.5 times

larger than the maximum load current to ensure that the

inductor does not saturate during normal operation. If

output short-circuit is a possible condition, the inductor

current should be rated to handle up to the peak current

speciﬁed for the buck-boost regulator.

TheinputcurrentlimitcomparatorwillshuttheinputPMOS

switchoffoncecurrentexceeds700mAtypical. Beforethe

switchcurrentlimit,theaveragecurrentlimitamp(620mA

typical) will source current into the feedback pin to drop

the output voltage. The input current limit also protects

against a short-circuit condition at the V

pin.

OUT2

Reverse Current Limit

The reverse current limit comparator will shut the output

PMOS switch off once current returning from the output

exceeds 450mA typical.

Output Overvoltage Protection

The inductor value also affects Burst Mode operation.

Lower inductor values will cause Burst Mode switching

frequencies to increase.

Ifthefeedbacknodewereinadvertentlyshortedtoground,

then the output would increase indeﬁnitely with the maxi-

mum current that could be sourced from the input supply.

The buck-boost regulator protects against this by shutting

off the input PMOS if the output voltage exceeds a 5.75V

maximum.

Differentcorematerialsandshapeswillchangethesize/cur-

rent and price/current relationship of an inductor. Toroid

or shielded pot cores in ferrite or permalloy materials

are small and do not radiate much energy, but cost more

than powdered iron core inductors with similar electrical

characteristics. Inductors that are very thin or have a very

small volume typically have much higher core and DCR

losses and will not give the best efﬁciency.

Buck-Boost Regulator Soft-Start Operation

Soft-start is accomplished by gradually increasing the

reference voltage over a 500μs typical period. A soft-

start cycle occurs whenever the buck-boost is enabled,

or after a fault condition has occurred (thermal shutdown

or UVLO). A soft-start cycle is not triggered by changing

operating modes. This allows seamless output operation

when transitioning between Burst Mode operation and

PWM mode operation.

Table 4 shows some inductors that work well with the

buck-boost regulator. These inductors offer a good com-

promise in current rating, DCR and physical size. Consult

each manufacturer for detailed information on their entire

selection of inductors.

Table 4. Recommended Inductors for the Buck-Boost Switching Regulator.

L

(μH)

MAX I

(A)

MAX DCR

(mΩ)

SIZE IN mm

(L × W × H)

DC

INDUCTOR TYPE

MANUFACTURER

DB3018C

D312C

DE2812C

2.4

2.2

2

1.31

1.14

1.4

80

140

81

Toko

www.toko.com

3.8 × 3.8 × 1.4

3.6 × 3.6 × 1.2

3 × 3.2 × 1.2

2.7

1.2

87

CDRH3D16

2.2

1.2

72

Sumida

www.sumida.com

4 × 4 × 1.8

SD12

2.2

1.8

74

Cooper

www.cooperet.com

5.2 × 5.2 × 1.2

*Typical DCR

3558f

28

LTC3558

APPLICATIONS INFORMATION

Buck-Boost Switching Regulator Input/Output

Capacitor Selection

PCB Layout Considerations

In order to deliver maximum charge current under all

conditions, it is critical that the backside of the LTC3558

be soldered to the PC board ground.

LowESR(equivalentseriesresistance)ceramiccapacitors

should be used at both the buck-boost regulator input

(PV )andtheoutput(V

).Itisrecommendedthatthe

IN2

OUT2

The LTC3558 has dual switching regulators. As with all

switching regulators, care must be taken while laying out

aPCboardandplacingcomponents. Theinputdecoupling

capacitors, the output capacitor and the inductors must all

be placed as close to the pins as possible and on the same

side of the board as the LTC3558. All connections must

also be made on the same layer. Place a local unbroken

ground plane below these components. Avoid routing

noisy high frequency lines such as those that connect to

switch pins over or parallel to lines that drive high imped-

ance inputs.

inputbebypassedwitha10μFcapacitor.Theoutputshould

be bypassed with at least a 10μF capacitor if using Type I

compensation and 22μF if using Type III compensation.

The same selection criteria apply for the buck-boost

regulator input and output capacitors as described in the

Buck Switching Regulator Input/Output Capacitor Selec-

tion section.

3558f

29

LTC3558

TYPICAL APPLICATIONS

UP TO 500mA

USB

V

BAT

CC

SINGLE

Li-lon CELL

(2.7V TO 4.2V)

(4.3V TO 5.5V)

+

10μF

PV

IN1

IN2

110k

OR AC ADAPTER

1

PV

NTC

10μF

4.7μF

28.7K

100k (NTC)

NTH50603NO1

LTC3558

510Ω

1.8V AT 400mA

10pF

4.7μH

SW1

CHRG

PROG

10μF

806k

1.74k

FB1

649k

SUSP

HPWR

EN1

SWAB2

2.2μH

DIGITAL

CONTROL

3.3V AT 400mA

SWCD2

V

OUT2

EN2

619k

200k

10μF

MODE

FB2

15k

150pF

GND2

(EXPOSED

PAD)

V

C2

GND

3558 TA02

Figure 12. Li-Ion to 3.3V at 400mA, 1.8V at 400mA and USB-Compatible Battery Charger

As shown in Figure 12, the LTC3558 can be operated

with no battery connected to the BAT pin. A 1Ω resistor

in series with a 4.7μF capacitor at the BAT pin ensures

in Figure 13. CHRG has a LED to provide a user with a

visual indication of battery charge status. The buck-boost

regulator starts up only after V is up to approximately

0.7V. This provides a sequencing function which may be

desirableinapplicationswhereamicroprocessorneedsto

bepoweredupbeforeperipherals.ATypeIIIcompensation

networkimprovesthetransientresponseofthebuck-boost

switching regulator.

OUT1

battery charger stability. 10μF V decoupling capacitors

CC

arerequiredforproperoperationoftheDC/DCconverters.

A three-resistor bias network for NTC sets hot and cold

trip points at approximately 55°C and 0°C.

The battery can be charged with up to 950mA of charge

current when powered from a 5V wall adaptor, as shown

3558f

30

LTC3558

PACKAGE DESCRIPTION

UD Package

20-Lead Plastic QFN (3mm × 3mm)

(Reference LTC DWG # 05-08-1720 Rev A)

0.70 ±0.05

3.50 ± 0.05

(4 SIDES)

1.65 ± 0.05

2.10 ± 0.05

PACKAGE

OUTLINE

0.20 ±0.05

0.40 BSC

RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS

APPLY SOLDER MASK TO AREAS THAT ARE NOT SOLDERED

BOTTOM VIEW—EXPOSED PAD

PIN 1 NOTCH

R = 0.20 TYP

OR 0.25 × 45°

CHAMFER

R = 0.115

TYP

0.75 ± 0.05

3.00 ± 0.10

(4 SIDES)

R = 0.05

TYP

19 20

PIN 1

TOP MARK

(NOTE 6)

0.40 ± 0.10

1

2

1.65 ± 0.10

(4-SIDES)

(UD20) QFN 0306 REV A

0.200 REF

0.20 ± 0.05

0.00 – 0.05

0.40 BSC

NOTE:

1. DRAWING IS NOT A JEDEC PACKAGE OUTLINE

2. DRAWING NOT TO SCALE

3. ALL DIMENSIONS ARE IN MILLIMETERS

4. DIMENSIONS OF EXPOSED PAD ON BOTTOM OF PACKAGE DO NOT INCLUDE

MOLD FLASH. MOLD FLASH, IF PRESENT, SHALL NOT EXCEED 0.15mm ON ANY SIDE

5. EXPOSED PAD SHALL BE SOLDER PLATED

6. SHADED AREA IS ONLY A REFERENCE FOR PIN 1 LOCATION

ON THE TOP AND BOTTOM OF PACKAGE

3558f

Information furnished by Linear Technology Corporation is believed to be accurate and reliable.

However, no responsibility is assumed for its use. Linear Technology Corporation makes no representa-

tion that the interconnection of its circuits as described herein will not infringe on existing patent rights.

31

LTC3558

TYPICAL APPLICATIONS

UP TO 950mA

4.7μH

5V WALL

ADAPTER

V

BAT

CC

SINGLE

Li-lon CELL

(2.7V TO 4.2V)

+

1μF

PV

IN1

100k

PV

10μF

IN2

NTC

1.2V AT 400mA

10pF

LTC3558

510Ω

100k (NTC)

SW1

10μF

324k

CHRG

PROG

FB1

887Ω

SWAB2

649k

SUSP

HPWR

MODE

EN1

2.2μH

DIGITAL

CONTROL

3.3V AT 400mA

SWCD2

V

OUT2

121k

33pF

22μF

10pF

324k

105k

EN2

FB2

15k

GND2

(EXPOSED

PAD)

330pF

GND

V

C2

Figure 13. Battery Charger Can Charge a Battery with Up to 950mA When Powered From a Wall Adapter

RELATED PARTS

PART NUMBER DESCRIPTION

COMMENTS

LTC3550

Dual Input USB/AC Adapter Li-Ion Battery Synchronous Buck Converter, Efﬁciency: 93%, Adjustable Output at 600mA, Charge Current:

Charger with Adjustable Output 600mA

Buck Converter

950mA Programmable, USB Compatible, Automatic Input Power Detection

and Selection

LTC3552

Standalone Linear Li-Ion Battery Charger

Synchronous Buck Converter, Efﬁciency: >90%, Adjustable Outputs at 800mA and

with Adjustable Output Dual Synchronous 400mA, Charge Current Programmable Up to 950mA, USB Compatible, 5mm × 3mm

Buck Converter

DFN-16 Package

LTC3552-1

LTC3455

Standalone Linear Li-Ion Battery Charger

with Dual Synchronous Buck Converter

Synchronous Buck Converter, Efﬁciency: >90%, Outputs 1.8V at 800mA and 1.575 at

400mA, Charge Current Programmable up to 950mA, USB Compatible

Dual DC/DC Converter with USB Power

Manager and Li-Ion Battery Charger

Seamless Transition Between Input Power Sources: Li-Ion Battery, USB and 5V Wall

Adapter, Two High Efﬁciency DC/DC Converters: Up to 96%, Full Featured Li-Ion Battery

Charger with Accurate USB Current Limiting (500mA/100mA) Pin-Selectable Burst Mode

Operation, Hot Swap^TMOutput for SDIO and Memory Cards, 4mm × 4mm QFN-24 Package

LTC3456

2-Cell, Multi-Output DC/DC Converter with Seamless Transition Between 2-Cell Battery, USB and AC Wall Adapter Input Power Sources,

USB Power Manager

Main Output: Fixed 3.3V Output, Core Output: Adjustable from 0.8V to V

, Hot Swap

BATT(MIN)

Output for Memory Cards, Power Supply Sequencing: Main and Hot Swap Accurate USB

Current Limiting, High Frequency Operation: 1MHz, High Efﬁciency: Up to 92%, 4mm ×

4mm QFN-24 Package

LTC3559

LTC4080

USB Charger with Dual Buck Regulators

Adjustable, Synchronous Buck Converters, Efﬁciency >90%, Outputs: Down to 0.8V at

400mA Each, Charge Current Programmable Up to 950mA, USB-Compatible, 3mm × 3mm

QFN-16 Package

500mA Standalone Charger with 300mA

Synchronous Buck

Charges Single-Cell Li-Ion Batteries, Timer Termination + C/10, Thermal Regulation, Buck

Output: 0.8V to V , Buck Input V : 2.7V to 5.5V, 3mm × 3mm DFN-10 Package

BAT

IN

Hot Swap is a trademark of Linear Technology Corporation.

3558f

LT 0408 • PRINTED IN USA

LinearTechnology Corporation

1630 McCarthy Blvd., Milpitas, CA 95035-7417

32

●

(408) 432-1900 FAX: (408) 434-0507 www.linear.com


型号：	LTC3558EUD-PBF
厂家：	Linear
描述：	Linear USB Battery Charger with Buck and Buck-Boost Regulators 线性USB电池充电器，降压和降压 - 升压型稳压器稳压器电池
文件：	总32页 (文件大小：398K)
中文：	中文翻译
下载：	下载PDF数据表文档文件

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