LTC3557EUF#PBF [Linear]
LTC3557/LTC3557-1 - USB Power Manager with Li-Ion Charger and Three Step-Down Regulators; Package: QFN; Pins: 28; Temperature Range: -40°C to 85°C;型号: | LTC3557EUF#PBF |
厂家: | Linear |
描述: | LTC3557/LTC3557-1 - USB Power Manager with Li-Ion Charger and Three Step-Down Regulators; Package: QFN; Pins: 28; Temperature Range: -40°C to 85°C |
文件: | 总28页 (文件大小:314K) |
中文: | 中文翻译 | 下载: | 下载PDF数据表文档文件 |
LTC3557/LTC3557-1
USB Power Manager with
Li-Ion Charger and Three
Step-Down Regulators
FEATURES
DESCRIPTION
The LTC®3557/LTC3557-1 is a highly integrated power
management and battery charger IC for single cell Li-Ion/
Polymer battery applications. It includes a PowerPathTM
manager with automatic load prioritization, a battery
charger, an ideal diode and numerous internal protection
features. Designed specifically for USB applications, the
LTC3557/LTC3557-1 power manager automatically limits
input current to a maximum of either 100mA or 500mA
for USB applications or 1A for wall adapter powered
applications. Battery charge current is automatically
reduced such that the sum of the load current and the
charge current does not exceed the programmed input
current limit. The LTC3557/LTC3557-1 also includes three
adjustable synchronous step-down switching regulators
and a high voltage buck regulator output controller with
Bat-Track that allows efficient charging from supplies as
high as 38V. The LTC3557/LTC3557-1 is available in a low
profile 4mm × 4mm × 0.75mm 28-pin QFN package.
■
Seamless Transition Between Input Power Sources:
Li-Ion Battery, USB, 5V Wall Adapter or High
Voltage Buck Regulator with Bat-TrackTM
200mΩ Internal Ideal Diode Plus Optional External
■
Ideal Diode Controller Provides Low Loss Power
Path When Input Current is Limited or Unavailable
■
Triple Adjustable High Efficiency Step-Down
Switching Regulators (600mA, 400mA, 400mA I
)
OUT
Pin Selectable Burst Mode® Operation
■
■
■
■
Full Featured Li-Ion/Polymer Battery Charger
1.5A Maximum Charge Current with Thermal Limiting
Battery Float Voltage:
4.2V (LTC3557)
4.1V (LTC3557-1)
Low Profile 4mm × 4mm 28-Pin QFN Package
■
APPLICATIONS
■
HDD-Based MP3 Players
, LT, LTC, LTM and Burst Mode are registered trademarks of Linear Technology
Corporation. Bat-Track and PowerPath are trademarks of Linear Technology Corporation.
All other trademarks are the property of their respective owners.
■
PDA, PMP, PND/GPS
■
USB-Based Handheld Products
Protected by U.S. Patents, including 6522118, 6700364. Other patents pending.
TYPICAL APPLICATION
Input and Battery Current vs Load Current
HV SUPPLY
HIGH VOLTAGE
BUCK DC/DC
8V TO 38V
(TRANSIENTS
TO 60V)
600
R
R
= 2k
PROG
CLPROG
I
= 2k
IN
500
400
300
200
100
0
100mA/500mA
1000mA
USB OR
I
V
LOAD
OUT
5V ADAPTER
0V
CC/CV
CHARGER
I
BAT
(CHARGING)
CHARGE
+
SINGLE CELL
Li-Ion
NTC
LTC3557/LTC3557-1
ALWAYS ON LDO
3.3V/25mA
I
BAT
(DISCHARGING)
400
500
WALL = 0V
100
0.8V to 3.6V/600mA
0.8V to 3.6V/400mA
0.8V to 3.6V/400mA
–100
TRIPLE HIGH EFFICIENCY
STEP-DOWN
600
0
200
300
(mA)
RST
SWITCHING REGULATORS
I
LOAD
35571 TA01b
35571 TA01a
35571fc
1
LTC3557/LTC3557-1
ABSOLUTE MAXIMUM RATINGS
PIN CONFIGURATION
(Notes 1-4)
V
, V , V , V
BUS OUT IN1 IN2
t < 1ms and Duty Cycle < 1% .................. −0.3V to 7V
TOP VIEW
Steady State............................................. −0.3V to 6V
28 27 26 25 24 23 22
BAT, NTC, CHRG, WALL, V ,
C
ILIM0
ILIM1
1
2
3
4
5
6
7
21 GATE
MODE, FB1, FB2, FB3, RST2........................ −0.3V to 6V
PROG
NTC
20
19
18
17
16
15
EN1, EN2, EN3 .............................. −0.3V to V
+ 0.3V
OUT
CC
WALL
ILIM0, ILIM1, PROG ....................... −0.3V to V + 0.3V
LDO3V3
SW1
V
29
NTC
I
I
I
I
I
, I
, I .........................................................2A
VBUS VOUT BAT
SW1
SW2 SW3
RST2 CHRG ACPR
SW3
.....................................................................850mA
V
V
IN2
IN1
FB1
SW2
, I
, I
............................................................600mA
, I
.................................................75mA
8
9
10 11 12 13 14
UF PACKAGE
, I
..........................................................2mA
CLPROG PROG
Maximum Operating Junction Temperature .......... 110°C
Operating Ambient Temperature Range ...−40°C to 85°C
Storage Temperature Range...................−65°C to 125°C
28-LEAD (4mm s 4mm) PLASTIC QFN
T
= 110°C, θ = 37°C/W
JMAX
JA
EXPOSED PAD (PIN 29) IS GND, MUST BE SOLDERED TO PCB
ORDER INFORMATION
LEAD FREE FINISH
LTC3557EUF#PBF
LTC3557EUF-1#PBF
TAPE AND REEL
PART MARKING
3557
PACKAGE DESCRIPTION
28-Lead (4mm × 4mm) Plastic QFN
28-Lead (4mm × 4mm) Plastic QFN
TEMPERATURE RANGE
−40°C to 85°C
−40°C to 85°C
LTC3557EUF#TRPBF
LTC3557EUF-1#TRPBF
35571
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/
POWER MANAGER ELECTRICAL CHARACTERISTICS
The ● denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C.
VBUS = 5V, VBAT = 3.8V, ILIM0 = ILIM1 = 5V, WALL = EN1 = EN2 = EN3 = 0V, RPROG = 2k, RCLPROG = 2.1k.
SYMBOL
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
Input Power Supply
V
Input Supply Voltage
4.35
5.5
V
BUS
I
Total Input Current (Note 5)
ILIM0 = 0V, ILIM1 = 0V (1x Mode)
ILIM0 = 5V, ILIM1 = 5V (5x Mode)
ILIM0 = 5V, ILIM1 = 0V (10x Mode)
80
450
900
90
475
950
100
500
1000
mA
mA
mA
BUS(LIM)
●
●
I
Input Quiescent Current
1x, 5x, 10x Modes
ILIM0 = 0V, ILIM1 = 5V (Suspend Mode)
0.35
0.05
mA
mA
BUSQ
0.1
h
Ratio of Measured V
Current to CLPROG 1x, 5x, 10x Modes
BUS
1000
mA/mA
CLPROG
Program Current
V
V
CLPROG Servo Voltage in Current Limit
1x Mode
5x Mode
10x Mode
0.2
1.0
2.0
V
V
V
CLPROG
UVLO
V
BUS
Undervoltage Lockout
Rising Threshold
Falling Threshold
3.8
3.7
3.9
V
V
3.5
35571fc
2
LTC3557/LTC3557-1
POWER MANAGER ELECTRICAL CHARACTERISTICS
The ● denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C.
VBUS = 5V, VBAT = 3.8V, ILIM0 = ILIM1 = 5V, WALL = EN1 = EN2 = EN3 = 0V, RPROG = 2k, RCLPROG = 2.1k.
SYMBOL
PARAMETER
to V Differential Undervoltage
OUT
CONDITIONS
MIN
TYP
MAX
UNITS
V
V
Rising Threshold
Falling Threshold
50
−50
100
mV
mV
DUVLO
BUS
Lockout
R
Input Current Limit Power FET
0.2
Ω
ON_LIM
On-Resistance (Between V
and V
)
OUT
BUS
Battery Charger
V
FLOAT
V
BAT
Regulated Output Voltage
LTC3557
4.179
4.165
4.079
4.065
4.200
4.200
4.100
4.100
4.221
4.235
4.121
4.135
V
V
V
V
LTC3557, 0°C ≤ T ≤ 85°C
A
LTC3557-1
LTC3557-1, 0°C ≤ T ≤ 85°C
A
●
●
●
I
I
Constant Current Mode Charge Current
R
R
R
= 1k, Input Current Limit = 2A
= 2k, Input Current Limit = 1A
= 5k, Input Current Limit = 400mA
950
465
180
1000
500
1050
535
mA
mA
mA
CHG
PROG
PROG
PROG
200
220
Battery Drain Current
V
BUS
V
BUS
> V
, Charger Off, I = 0μA
OUT
6
55
27
100
μA
μA
BAT
UVLO
= 0V, I
= 0μA (Ideal Diode Mode)
OUT
V
V
PROG Pin Servo Voltage
PROG Pin Servo Voltage in Trickle Charge
1.000
0.100
V
V
PROG
PROG(TRKL)
BAT < V
TRKL
h
Ratio of I to PROG Pin Current
1000
50
mA/mA
mA
PROG
TRKL
BAT
I
Trickle Charge Current
BAT < V
40
60
TRKL
V
Trickle Charge Rising Threshold
Trickle Charge Falling Threshold
BAT Rising
BAT Falling
2.85
2.75
3.0
V
V
TRKL
2.5
−75
3.2
Recharge Battery Threshold Voltage
Safety Timer Termination Period
Threshold Voltage Relative to V
mV
Hour
ΔV
−100
4
−115
4.8
FLOAT
RECHRG
t
Timer Starts when BAT = V
– 50mV
TERM
BADBAT
FLOAT
t
Bad Battery Termination Time
BAT < V
0.4
0.5
0.1
200
0.6
Hour
TRKL
h
C/10
End-of-Charge Indication Current Ratio
(Note 6)
0.085
0.115
mA/mA
mΩ
R
Battery Charger Power FET On-Resistance
ON(CHG)
(Between V
and BAT)
OUT
T
Junction Temperature in Constant
Temperature Mode
110
°C
LIM
NTC
V
V
V
I
Cold Temperature Fault Threshold Voltage
Hot Temperature Fault Threshold Voltage
NTC Disable Threshold Voltage
NTC Leakage Current
Rising NTC Voltage
Hysteresis
75
34
76
77
36
2.2
50
%V
%V
COLD
HOT
DIS
VNTC
VNTC
1.3
Falling NTC Voltage
Hysteresis
35
1.3
%V
%V
VNTC
VNTC
●
Falling NTC Voltage
Hysteresis
1.2
−50
1.7
50
%V
VNTC
mV
NTC = V
= 5V
nA
NTC
BUS
Ideal Diode
V
Forward Voltage Detection
Diode On-Resistance, Dropout
Diode Current Limit
I
I
= 10mA
= 1A
5
15
200
3.6
25
mV
mΩ
A
FWD
OUT
R
DROPOUT
MAX
OUT
I
(Note 7)
Always On 3.3V Supply
V
Regulated Output Voltage
0mA < I
< 25mA
3.1
3.3
24
3.5
V
Ω
Ω
LDO3V3
LDO3V3
R
R
Open-Loop Output Resistance
Closed-Loop Output Resistance
BAT = 3.0V, V
= 0V
OL(LDO3V3)
CL(LDO3V3)
BUS
3.2
35571fc
3
LTC3557/LTC3557-1
POWER MANAGER ELECTRICAL CHARACTERISTICS
The ● denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C.
VBUS = 5V, VBAT = 3.8V, ILIM0 = ILIM1 = 5V, WALL = EN1 = EN2 = EN3 = 0V, RPROG = 2k, RCLPROG = 2.1k.
SYMBOL
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
Wall Adapter
V
ACPR
ACPR Pin Output High Voltage
ACPR Pin Output Low Voltage
I
I
= 1mA
= 1mA
V
OUT
0
V
V
V
OUT
− 0.3
ACPR
ACPR
0.3
V
Absolute Wall Input Threshold Voltage
Differential Wall Input Threshold Voltage
Wall Operating Quiescent Current
WALL Rising
WALL Falling
4.3
3.2
4.45
V
V
W
3.1
0
25
75
mV
mV
ΔV
WALL − BAT Falling
WALL − BAT Rising
W
150
0.4
I
440
μA
I
+ I
, I = 0mA,
VOUT BAT
OUT
QWALL
WALL
WALL = V
= 5V
Logic (I
, I
and CHRG)
LIM0 LIM1
V
V
Input Low Voltage
ILIM0, ILIM1
ILIM0, ILIM1
V
V
IL
IH
Input High Voltage
1.2
I
Static Pull-Down Current
CHRG Pin Output Low Voltage
CHRG Pin Input Current
ILIM0, ILIM1; V = 1V
2
0.15
0
μA
V
PD
PIN
V
I
= 10mA
0.4
1
CHRG
CHRG
CHRG
I
BAT = 4.5V, CHRG = 5V
μA
SWITCHING REGULATOR ELECTRICAL CHARACTERISTICS
The ● denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C.
VOUT = VIN1 = VIN2 = 3.8V, MODE = EN1 = EN2 = EN3 = 0V.
SYMBOL
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
Step-Down Switching Regulators 1, 2 and 3
●
V
V
, V
Input Supply Voltage
(Note 9)
2.7
2.5
5.5
2.9
V
IN1 IN2
UVL0
V
OUT
V
OUT
Falling
Rising
V
and V Connected to V Through Low
OUT
2.7
2.8
V
V
OUT
IN1
IN2
Impedance. Switching Regulators are Disabled
Below V UVLO
OUT
f
Oscillator Frequency
Input Low Voltage
1.91
1.2
2.25
2.59
0.4
MHz
V
OSC
V
V
MODE, EN1, EN2, EN3
MODE, EN1, EN2, EN3
IL
IH
Input High Voltage
V
I
Static Pull-Down Current
MODE, EN1, EN2, EN3 (V = 1V)
1
μA
PD
PIN
Step-Down Switching Regulator 1
I
Pulse-Skip Mode Input Current (Note 10)
Burst Mode Input Current (Note 10)
Shutdown Input Current
I
I
I
= 0, EN1 = 3.8V, MODE = 0V
= 0, EN1 = MODE = 3.8V
= 0, EN1 = 0V, FB1 = 0V
220
35
μA
μA
VIN1
OUT
OUT
OUT
50
1
0.01
1200
μA
I
Peak PMOS Current Limit
EN1 = 3.8V, MODE = 0V or 3.8V (Note 7)
900
1500
mA
LIM1
●
●
V
I
Feedback Voltage
EN1 = 3.8V, MODE = 0V
EN1 = MODE = 3.8V
0.78
0.78
0.8
0.8
0.82
V
V
FB1
0.824
FB1 Input Current (Note 10)
Maximum Duty Cycle
EN1 = 3.8V
0.05
μA
%
−0.05
FB1
D1
FB1 = 0V, EN1 = 3.8V
EN1 = 3.8V
100
R
R
R
R
R
of PMOS
of NMOS
0.3
0.4
10
Ω
P1
DS(ON)
DS(ON)
EN1 = 3.8V
Ω
N1
SW1 Pull-Down in Shutdown
EN1 = 0V
kΩ
SW1(PD)
35571fc
4
LTC3557/LTC3557-1
SWITCHING REGULATOR ELECTRICAL CHARACTERISTICS
The ● denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C.
VOUT = VIN1 = VIN2 = 3.8V, MODE = EN1 = EN2 = EN3 = 0V.
SYMBOL
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
Step-Down Switching Regulator 2
I
Pulse-Skip Mode Input Current (Note 10)
Burst Mode Input Current (Note 10)
Shutdown Input Current
I
I
I
= 0, EN2 = 3.8V, MODE = 0V
= 0, EN2 = MODE = 3.8V
= 0, EN2 = 0V, FB2 = 0V
220
35
μA
μA
VIN2
OUT
OUT
OUT
50
1
0.01
800
μA
I
Peak PMOS Current Limit
EN2 = 3.8V, MODE = 0V or 3.8V (Note 7)
600
1000
mA
LIM2
●
●
V
I
Feedback Voltage
EN2 = 3.8V, MODE = 0V
EN2 = MODE = 3.8V
0.78
0.78
0.8
0.8
0.82
V
V
FB2
0.824
FB2 Input Current (Note 10)
Maximum Duty Cycle
EN2 = 3.8V
0.05
μA
%
−0.05
FB2
D2
FB2 = 0V, EN2 = 3.8V
EN2 = 3.8V
100
R
R
R
R
R
of PMOS
of NMOS
0.6
0.6
10
Ω
P2
DS(ON)
DS(0N)
EN2 = 3.8V
Ω
N2
SW2 Pull-Down in Shutdown
EN2 = 0V
kΩ
V
SW2(PD)
RST2
RST2
V
Power-On RST2 Pin Output Low Voltage
I
= 1mA, FB2 = 0V, EN2 = 3.8V
= 5.5V, EN2 = 3.8V
0.1
0.35
1
RST2
I
Power-On RST2 Pin Input Current (Note 10) V
μA
%
RST2
V
Power-On RST2 Pin Threshold
Power-On RST2 Pin Delay
(Note 8)
−8
TH(RST2)
t
From RST2 Threshold to RST2 Hi-Z
230
ms
RST2
Step-Down Switching Regulator 3
I
Pulse-Skip Mode Input Current (Note 10)
Burst Mode Input Current (Note 10)
Shutdown Input current
I
I
I
= 0, EN3 = 3.8V, MODE = 0V
= 0, EN3 = MODE = 3.8V
= 0, EN3 = 0V, FB3 = 0V
220
35
μA
μA
VIN2
OUT
OUT
OUT
50
1
0.01
800
μA
I
Peak PMOS Current Limt
EN3 = 3.8V, MODE = 0V or 3.8V (Note 7)
600
1000
mA
LIM3
●
●
V
I
Feedback Voltage
EN3 = 3.8V, MODE = 0V
EN3 = MODE = 3.8V
0.78
0.78
0.8
0.8
0.82
V
V
FB3
0.824
FB3 Input Current (Note 10)
Maximum Duty Cycle
EN3 = 3.8V
0.05
μA
%
−0.05
FB3
D3
FB3 = 0V, EN3 = 3.8V
EN3 = 3.8V
100
R
R
R
R
R
of PMOS
of NMOS
0.6
0.6
10
Ω
P3
DS(ON)
DS(ON)
EN3 = 3.8V
Ω
N3
SW3 Pull-Down in Shutdown
EN3 = 0V
kΩ
SW3(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 5. Total input current is the sum of quiescent current, I
, and
BUSQ
measured current given by V
/R
• (h
+ 1)
CLPROG CLPROG
CLPROG
Note 6. h
is expressed as a fraction of measured full charge current
C/10
with indicated PROG resistor.
Note 2. The LTC3557/LTC3557-1 is guaranteed to meet performance
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.
Note 7. The current limit features of this part are intended to protect the
IC from short term or intermittent fault conditions. Continuous operation
above the maximum specified pin current rating may result in device
degradation or failure.
Note 3. This IC includes overtemperature protection that is intended
to protect the device during momentary overload conditions. Junction
temperatures will exceed 110°C when overtemperature protection is
active. Continuous operation above the specified maximum operating
junction temperature may result in device degradation or failure.
Note 8. RST2 threshold is expressed as a percentage difference from the
FB2 regulation voltage. The threshold is measured for FB2 rising.
Note 9. V
not in UVLO.
OUT
Note 10. FB high, not switching.
Note 4. V is the greater of V , V
or BAT.
CC
BUS OUT
35571fc
5
LTC3557/LTC3557-1
TYPICAL PERFORMANCE CHARACTERISTICS TA = 25°C unless otherwise specified
Input Supply Current
vs Temperature
Input Supply Current
Battery Drain Current
vs Temperature
vs Temperature (Suspend Mode)
0.20
0.18
0.16
0.14
0.12
0.10
0.08
0.06
0.04
0.02
0
0.10
0.08
0.06
0.04
0.02
0
0.8
V
BUS
= 5V
V
= 5V
BUS
3 BUCKS ENABLED
2 BUCKS ENABLED
1x MODE
0.7
0.6
0.5
0.4
0.3
0.2
0.1
1 BUCK ENABLED
N0 BUCKS ENABLED
V
= 3.8V
BAT
MODE = 3.8V
0
–50 –25
0
50
75 100 125
–50
–25
0
25
50
75 100 125
25
–25
0
50
75 100 125
–50
25
TEMPERATURE (°C)
TEMPERATURE (°C)
TEMPERATURE (°C)
35571 G03
35571 G02
35571 G01
Input Current Limit
vs Temperature
Charge Current vs Temperature
(Thermal Regulation)
Input RON vs Temperature
1200
1100
1000
900
800
700
600
500
400
300
200
100
0
300
280
260
240
220
180
160
140
120
100
0
600
500
400
300
V
= 5V
CLPROG
I
= 400mA
BUS
OUT
R
= 2.1k
10x MODE
V
BUS
= 4.5V
V
BUS
= 5V
5x MODE
V
BUS
= 5.5V
200
100
0
V
= 5V
BUS
1x MODE
10x MODE
= 2k
R
PROG
–50
0
25
50
75 100 125
–25
–50
0
25
50
75 100 125
–25
50
TEMPERATURE (°C)
100 125
–50 –25
0
25
75
TEMPERATURE (°C)
TEMPERATURE (°C)
35571 G04
35571 G05
35571 G06
Battery Current and Voltage
vs Time (LTC3557)
Battery Regulation (Float)
Voltage vs Temperature
VFLOAT Load Regulation
4.22
4.20
4.18
4.16
4.14
4.12
4.10
4.08
4.06
600
500
400
300
200
100
0
6
5
4
3
2
1
0
4.22
4.20
4.18
4.16
I
= 2mA
LTC3557
V
= 5V
BAT
BUS
LTC3557
10x MODE
CHRG
V
BAT
4.14
4.12
SAFETY
TIMER
LTC3557-1
1450mAhr
CELL
TERMINATION
LTC3557-1
4.10
4.08
4.06
C/10
V
= 5V
BUS
PROG
R
R
= 2k
= 2k
I
BAT
CLPROG
200
400
800
50
TEMPERATURE (°C)
125
0
2
3
4
5
6
0
1000
–50
0
25
75 100
1
600
(mA)
–25
TIME (HOUR)
I
BAT
35571 G07
35571 G08
35571 G09
35571fc
6
LTC3557/LTC3557-1
TYPICAL PERFORMANCE CHARACTERISTICS TA = 25°C unless otherwise specified
Forward Voltage
vs Ideal Diode Current
(with Si2333DS External FET)
Forward Voltage vs Ideal Diode
Current (No External FET)
IBAT vs VBAT
600
500
400
300
200
100
0
40
35
30
25
0.25
0.20
0.15
0.10
V
T
= 0V
V
V
A
= 3.8V
= 0V
BUS
A
BAT
BUS
= 25°C
= 25°C
V
= 3.2V
BAT
T
V
= 3.6V
BAT
V
BAT
= 4.2V
20
15
10
5
V
= 5V
BUS
0.05
0
10x MODE
R
R
= 2k
CLPROG
PROG
= 2k
0
0.2
0.4
I
0.8
0
1.0
2.0
2.8
3.2
(V)
3.6
4.0
4.4
0.6
(A)
2.4
0
0.4
0.6
(A)
0.8
1.0
1.2
0.2
V
BAT
I
BAT
BAT
35571 G12
35571 G10
35571 G11
Input Connect Waveform
Input Disconnect Waveform
Switching from 1x to 5x Mode
V
V
BUS
5V/DIV
BUS
5V/DIV
ILIM0/ILIM1
5V/DIV
V
V
OUT
OUT
5V/DIV
5V/DIV
I
I
I
BUS
BUS
BUS
0.5A/DIV
0.5A/DIV
0.5A/DIV
I
I
I
BAT
0.5A/DIV
BAT
BAT
0.5A/DIV
0.5A/DIV
35571 G25
35571 G26
35571 G27
V
= 3.75V
1ms/DIV
V
= 3.75V
1ms/DIV
V
= 3.75V
= 50mA
1ms/DIV
BAT
OUT
BAT
OUT
BAT
OUT
I
= 100mA
I
= 100mA
I
R
R
= 2k
R
R
= 2k
R
R
= 2k
CLPROG
CLPROG
CLPROG
= 2k
= 2k
= 2k
PROG
PROG
PROG
Switching from Suspend Mode
to 5x Mode
WALL Connect Waveform
WALL Disconnect Waveform
ILIM0
5V/DIV
WALL
5V/DIV
WALL
5V/DIV
V
OUT
5V/DIV
V
V
OUT
OUT
5V/DIV
5V/DIV
I
I
WALL
0.5A/DIV
WALL
I
BUS
0.5A/DIV
0.5A/DIV
I
I
I
BAT
BAT
BAT
0.5A/DIV
0.5A/DIV
0.5A/DIV
35571 G28
35571 G29
35571 G30
V
= 3.75V
100μs/DIV
V
= 3.75V
1ms/DIV
V
= 3.75V
1ms/DIV
BAT
OUT
BAT
OUT
BAT
OUT
I
= 100mA
I
= 100mA
I
= 100mA
R
R
= 2k
R
= 2k
R
= 2k
PROG
CLPROG
PROG
= 2k
PROG
ILIM1 = 5V
35571fc
7
LTC3557/LTC3557-1
TYPICAL PERFORMANCE CHARACTERISTICS TA = 25°C unless otherwise specified
Oscillator Frequency
vs Temperature
Step-Down Switching Regulator 1
3.3V Output Efficiency vs IOUT1
Step-Down Switching Regulator 2
1.2V Output Efficiency vs IOUT2
2.5
2.4
2.3
2.2
2.1
2.0
1.9
1.8
1.7
1.6
1.5
100
90
100
90
Burst Mode
OPERATION
Burst Mode
OPERATION
V
= 3.8V
= 5V
80
IN
80
V
IN
70
70
60
50
60
50
PULSE SKIP
PULSE SKIP
40
30
20
10
0
40
30
20
10
0
V
IN
= 2.9V
V
IN
= 2.7V
V
OUT1
= 3.3V
V
= 1.2V
OUT2
V
IN1
= 3.8V
= 5V
V
V
= 3.8V
= 5V
IN1
IN2
IN2
V
–50
0
25
50
75 100 125
–25
0.01
0.1
1
I
10
100
1000
0.01
0.1
1
I
10
100
1000
TEMPERATURE (°C)
(mA)
(mA)
OUT1
OUT2
35571 G14
35571 G15
35571 G13
Step-Down Switching
Regulator Short-Circuit Current
vs Temperature
Step-Down Switching Regulator
Pulse Skip Supply Current vs VINX
Step-Down Switching Regulator 3
1.8V Output Efficiency vs IOUT3
100
90
400
350
1200
V
= 1.2V
= 0mA
OUTX
OUTX
I
1100
1000
Burst Mode
OPERATION
80
110°C
600mA BUCK
400mA BUCK
70
300
250
900
800
700
600
500
60
50
PULSE SKIP
75°C
25°C
40
30
20
10
0
200
150
100
–45°C
V
OUT3
= 1.8V
V
V
= 3.8V
= 5V
IN3
IN3
400
2.5
3.0
3.5
V
4.0
(V)
4.5
5.0
–25
0
50
75 100 125
0.01
0.1
1
I
10
100
1000
–50
25
(mA)
TEMPERATURE (°C)
INX
OUT3
35571 G16
35571 G17
35571 G18
Step-Down Switching Regulator
Output Transient (MODE = 1)
Step-Down Switching Regulator
Output Transient (MODE = 0)
Step-Down Switching Regulator
Switch Impedance vs Temperature
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
V
INX
= 3.2V
V
V
OUT2
OUT2
50mV/DIV
(AC)
50mV/DIV
(AC)
400mA
PMOS
400mA
NMOS
V
V
OUT3
OUT3
50mV/DIV
(AC)
50mV/DIV
(AC)
600mA PMOS
600mA NMOS
300mA
300mA
I
I
OUT2
OUT2
5mA
5mA
35571 G1
35571 G2
V
V
I
= 1.2V
= 1.8V
50μs/DIV
V
V
I
= 1.2V
= 1.8V
50μs/DIV
OUT2
OUT3
OUT3
OUT2
OUT3
OUT3
= 16mA
= 100mA
0
–50 –25
0
25
125
50
75 100
TEMPERATURE (°C)
35571 G21
35571fc
8
LTC3557/LTC3557-1
TYPICAL PERFORMANCE CHARACTERISTICS TA = 25°C unless otherwise specified
600mA Step-Down Switching
Regulator Feedback Voltage
vs Output Current
400mA Step-Down Switching
Regulator Feedback Voltage
vs Output Current
Step-Down Switching Regulator
Start-Up Waveform
0.85
0.84
0.83
0.82
0.81
0.80
0.79
0.78
0.77
0.76
0.75
0.85
0.84
0.83
0.82
0.81
0.80
0.79
0.78
0.77
0.76
0.75
V
OUT2
50mV/DIV(AC)
Burst Mode
OPERATION
Burst Mode
OPERATION
V
OUT1
1V/DIV
0V
PULSE SKIP
I
PULSE SKIP
L1
200mA/DIV
0mA
EN1
35571 G24
V
= 1.2V
100μs/DIV
OUT2
OUT2
3.8V
5V
3.8V
5V
I
= 50mA
MODE = 1
R
= 8Ω
OUT1
0.1
1
10
100
1000
0.1
1
10
100
1000
OUTPUT CURRENT (mA)
OUTPUT CURRENT (mA)
35571 G22
35571 G23
PIN FUNCTIONS
ILIM0,ILIM1(Pins1,2):InputCurrentControlPins.ILIM0
andILIM1controltheinputcurrentlimit. SeeTable1. Both
pinsarepulledlowbyaweakcurrentsink.
MODE (Pin 8): Low Power Mode Enable. When this pin is
pulled high, the three step-down switching regulators are
settolowpowerBurstModeoperation.
EN1 (Pin 9): Logic Input Enables Step-Down Switching
WALL (Pin 3): Wall Adapter Present Input. Pulling this pin
Regulator1.
above 4.3V will disconnect the power path from V
to
BUS
V
. TheACPRpinwillalsobepulledlowtoindicatethata
OUT
EN2 (Pin 10): Logic Input Enables Step-Down Switching
Regulator2.
walladapterhasbeendetected.
LDO3V3 (Pin 4): Always On 3.3V LDO Output. The
EN3 (Pin 11): Logic Input Enables Step-Down Switching
LDO3V3 pin provides a regulated, always-on 3.3V supply
Regulator3.
voltage. This pin gets its power from V . It may be used
OUT
FB3 (Pin 12): Feedback Input for Step-Down Switching
Regulator3.Thispinservostoafixedvoltageof0.8Vwhen
thecontrolloopiscomplete.
for light loads such as a real-time clock or housekeeping
microprocessor. A 1μF capacitor is required from LDO3V3
to ground if it will be called upon to deliver current. If
the LDO3V3 output is not used it should be disabled by
FB2 (Pin 13): Feedback Input for Step-Down Switching
Regulator2.Thispinservostoafixedvoltageof0.8Vwhen
thecontrolloopiscomplete.
connecting it to V
.
OUT
SW1 (Pin 5): Power Transmission (Switch) Pin for
Step-DownSwitchingRegulator1.
RST2(Pin14):Thisisanopen-drainoutputwhichindicates
thatstep-downswitchingregulator2hassettledtoitsfinal
value. It can be used as a power on reset for the primary
microprocessor or to enable the other buck regulators for
supplysequencing.
V
(Pin 6): Power Input for Step-Down Switching
IN1
Regulator1.ThispinwillgenerallybeconnectedtoV
.
OUT
FB1 (Pin 7): Feedback Input for Step-Down Switching
Regulator1.Thispinservostoafixedvoltageof0.8Vwhen
thecontrolloopiscomplete.
SW2 (Pin 15): Power Transmission (Switch) Pin for
Step-DownSwitchingRegulator2.
35571fc
9
LTC3557/LTC3557-1
PIN FUNCTIONS
V
(Pin16):PowerInputforStep-DownSwitchingRegu-
exceeds the allotted input current from V
or if the V
BUS
IN2
BUS
lators2and3.ThispinwillgenerallybeconnectedtoV
.
power source is removed. V
should be bypassed with
OUT
OUT
a low impedance multilayer ceramic capacitor. The total
capacitance on V should maintain a minimum of 5μF
SW3 (Pin 17): Power Transmission (Switch) Pin for
OUT
Step-DownSwitchingRegulator3.
overoperatingvoltageandtemperature.
V
(Pin18):OutputBiasVoltageforNTC.Aresistorfrom
NTC
V
(Pin 24): USB Input Voltage. V
will usually be
BUS
BUS
thispintotheNTCpinwillbiastheNTCthermistor.
connectedtotheUSBportofacomputeroraDCoutputwall
NTC(Pin19):TheNTCpinconnectstoabattery’sthermistor
todetermineifthebatteryistoohotortoocoldtocharge.If
thebattery’stemperatureisoutofrange,chargingispaused
until it drops back into range. A low drift bias resistor is
adapter. V
multilayerceramiccapacitor.
should be bypassed with a low impedance
BUS
ACPR (Pin 25): Wall Adapter Present Output (Active
Low). A low on this pin indicates that the wall adapter
input comparator has had its input pulled above its input
threshold(typically4.3V). Thispincanbeusedtodrivethe
gateofanexternalP-channelMOSFETtoprovidepowerto
requiredfromV toNTCandathermistorisrequiredfrom
NTC
NTC to ground. If the NTC function is not desired, the NTC
pinshouldbegrounded.
PROG (Pin 20): Charge Current Program and Charge
Current Monitor Pin. Connecting a resistor from PROG to
groundprogramsthechargecurrent:
V
fromapowersourceotherthanaUSBport.
OUT
V (Pin26):HighVoltageBuckRegulatorControlPin.This
C
pin can be used to drive the V pin of an approved external
C
1000V
ICHG(A)=
highvoltagebuckswitchingregulator.AnexternalP-channel
MOSFET is required to provide power to V
with its gate
RPROG
OUT
tiedtotheACPRpin.TheV pinisdesignedtoworkwiththe
C
LT®3480,LT3481andLT3505.
If sufficient input power is available in constant current
mode, this pin servos to 1V. The voltage on this pin always
representstheactualchargecurrent.
CLPROG(Pin27):InputCurrentProgramandInputCurrent
MonitorPin.AresistorfromCLPROGtogrounddetermines
GATE (Pin 21): Ideal Diode Gate Connection. This pin
controlsthegateofanoptionalexternalP-channelMOSFET
transistorusedtosupplementtheinternalidealdiode. The
source of the P-channel MOSFET should be connected
the upper limit of the current drawn from the V
pin
BUS
(i.e., the input current limit). A precise fraction of the input
current, h , is sent to the CLPROG pin. The input
CLPROG
PowerPath delivers current until the CLPROG pin reaches
to V
and the drain should be connected to BAT. It is
2.0V (10x Mode), 1.0V (5x Mode) or 0.2V (1x Mode).
OUT
important to maintain high impedance on this pin and
minimizeallleakagepaths.
Therefore,thecurrentdrawnfromV willbelimitedtoan
BUS
amountgivenbyh
andR
.InUSBapplications
CLPROG
CLPROG
theresistorR
shouldbesettonolessthan2.1k.
CLPROG
BAT (Pin 22): Single Cell Li-Ion Battery Pin. Depending on
availablepowerandload,aLi-IonbatteryonBATwilleither
CHRG (Pin 28): 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., float charge current less than 1/10th
programmedchargecurrent),unresponsivebattery(i.e.,its
voltageremainsbelow2.8Vafter1/2hourofcharging)and
battery temperature out of range. CHRG requires a pull-up
resistorand/orLEDtoprovideindication.
deliversystempowertoV
throughtheidealdiodeorbe
OUT
chargedfromthebatterycharger.
V
(Pin23):OutputVoltageofthePowerPathController
OUT
and Input Voltage of the Battery Charger. The majority of
the portable product should be powered from V . The
OUT
LTC3557/LTC3557-1 will partition the available power
between the external load on V
and the internal battery
OUT
charger. Priority is given to the external load and any extra
power is used to charge the battery. An ideal diode from
Exposed Pad (Pin 29): Ground. The exposed package pad
is ground and must be soldered to the PC board for proper
BAT to V
ensures that V
is powered even if the load
functionalityandformaximumheattransfer.
OUT
OUT
35571fc
10
LTC3557/LTC3557-1
BLOCK DIAGRAM
3
25
ACPR
26
WALL
V
C
WALL
DETECT
V
C
CONTROL
V
V
BUS
OUT
24
23
21
+
–
GATE
IDEAL
DIODE
CC/CV
CHARGER
INPUT
CURRENT
LIMIT
CLPROG
27
–
+
15mV
BAT
22
20
PROG
LDO3V3
3.3V
LDO
4
6
V
IN1
V
NTC
BATTERY
18
19
TEMP
600mA, 2.25MHz
NTC
MONITOR
BUCK REGULATOR
OSC
EN
REF
SW1
FB1
CHRG
5
28
CHARGE
STATUS
MODE
7
V
IN2
16
ILIM0
ILIM1
1
2
ILIM
LOGIC
400mA, 2.25MHz
BUCK REGULATOR
OSC
EN1
SW2
FB2
9
15
13
EN2
EN
LOGIC
10
11
8
EN
EN3
MODE
MODE
RST2
14
400mA, 2.25MHz
BUCK REGULATOR
OSC
SW3
FB3
17
12
EN
MODE
GND
29
35571 BD
35571fc
11
LTC3557/LTC3557-1
OPERATION
Introduction
The LTC3557/LTC3557-1 has the unique ability to use
the output, which is powered by an external supply, to
charge the battery while providing power to the load. A
comparator on the WALL pin is configured to detect the
presence of the wall adapter and shut off the connection
The LTC3557/LTC3557-1 is a highly integrated power
management IC that includes a PowerPath controller,
battery charger, an ideal diode, an always-on LDO, three
synchronous step-down switching regulators as well as
to the USB. This prevents reverse conduction from V
OUT
a buck regulator V controller. Designed specifically for
C
to V
when a wall adapter is present.
BUS
USB applications, the PowerPath controller incorporates
a precision input current limit which communicates with
the battery charger to ensure that input current never
violates the USB specifications.
The LTC3557/LTC3557-1 provides a V output pin which
C
can be used to drive the V pin of an external high voltage
C
buck switching regulator such as the LT3480, LT3481, or
LT3505 to provide power to the V
pin. The V control
OUT
C
The ideal diode from BAT to V
guarantees that ample
OUT
OUT
circuitry adjusts the regulation point of the switching
regulator to a small voltage above the BAT pin voltage.
This control method provides a high input voltage, high
efficiency battery charger and PowerPath function.
powerisalwaysavailabletoV evenifthereisinsufficient
or absent power at V
.
BUS
The LTC3557/LTC3557-1 also has the ability to receive
power from a wall adapter or other non-current-limited
power source. Such a power supply can be connected
An “always on” LDO provides a regulated 3.3V from V
.
OUT
This LDO will be on at all times and can be used to supply
up to 25mA.
to the V
pin of the LTC3557/LTC3557-1 through an
OUT
external device such as a power Schottky or FET as shown
in Figure 1.
FROM AC ADAPTER (OR HIGH VOLTAGE BUCK OUTPUT)
26
V
C
OPTIONAL CONTROL
FOR HIGH VOLTAGE BUCK REGS
LT3480, LT3481 OR LT3505
4.3V
(RISING)
3.2V
–
+
(FALLING)
WALL
ACPR
3
25
+
–
75mV (RISING)
25mV (FALLING)
+
–
FROM
USB
ENABLE
V
BUS
V
V
OUT
OUT
24
23
21
SYSTEM
LOAD
USB CURRENT LIMIT
IDEAL
DIODE
OPTIONAL
EXTERNAL
IDEAL DIODE
PMOS
+
–
GATE
CONSTANT CURRENT
CONSTANT VOLTAGE
BATTERY CHARGER
–
+
15mV
BAT
BAT
22
+
Li-Ion
35571 F01
Figure 1. Simplified PowerPath Block Diagram
35571fc
12
LTC3557/LTC3557-1
OPERATION
TheLTC3557/LTC3557-1includesthree2.25MHzconstant
frequency current mode step-down switching regulators
providing 400mA, 400mA and 600mA each. All step-
down switching regulators can be programmed for a
minimumoutputvoltageof0.8Vandcanbeusedtopower
a microcontroller core, microcontroller I/O, memory or
other logic circuitry. All step-down switching regulators
support 100% duty cycle operation and are capable of
operating in Burst Mode operation for highest efficiencies
at light loads (Burst Mode operation is pin selectable). No
external compensation components are required for the
switching regulators.
The input current limit is programmed by the ILIM0 and
ILIM1 pins. The LTC3557/LTC3557-1 can be configured to
limitinputcurrenttooneofseveralpossiblesettingsaswell
as be deactivated (USB Suspend). The input current limit
willbesetbytheappropriateservovoltageandtheresistor
on CLPROG according to the following expression:
0.2V
RCLPROG
IVBUS = IBUSQ
IVBUS = IBUSQ
IVBUS = IBUSQ
+
+
+
• hCLPROG 1x Mode
(
)
1V
RCLPROG
• hCLPROG 5x Mode
(
)
2V
RCLPROG
USB PowerPath Controller
• hCLPROG 10x Mode
(
)
The input current limit and charge control circuits of the
LTC3557/LTC3557-1 are designed to limit input current
as well as control battery charge current as a function of
Underworst-caseconditions,theUSBspecificationwillnot
be violated with an R resistor of greater than 2.1k.
CLPROG
I
. V
drives the combination of the external load,
VOUT OUT
Table 1 shows the available settings for the ILIM0 and
ILIM1 pins:
the three step-down switching regulators, always on 3.3V
LDO and the battery charger.
Table 1: Controlled Input Current Limit
If the combined load does not exceed the programmed
ILIM1
ILIM0
I
BUS(LIM)
inputcurrentlimit,V
willbeconnectedtoV
through
OUT
BUS
0
0
1
1
0
1
0
1
100mA (1x)
1A (10x)
an internal 200mΩ P-channel MOSFET.
If the combined load at V exceeds the programmed
OUT
Suspend
inputcurrentlimit,thebatterychargerwillreduceitscharge
current by the amount necessary to enable the external
load to be satisfied while maintaining the programmed
input current. Even if the battery charge current is set to
exceedtheallowableUSBcurrent,theaverageinputcurrent
USB specification will not be violated. Furthermore, load
500mA (5x)
Notice that when ILIM0 is high and ILIM1 is low, the input
current limit is set to a higher current limit for increased
charging and current availability at V . This mode is
OUT
typically used when there is power available from a wall
current at V
will always be prioritized and only excess
OUT
adapter.
available current will be used to charge the battery.
Ideal Diode from BAT to V
ThecurrentoutoftheCLPROGpinisafraction(1/h
)
OUT
CLPROG
of the V
current. When a programming resistor is con-
BUS
TheLTC3557/LTC3557-1hasaninternalidealdiodeaswell
as a controller for an optional external ideal diode. Both
the internal and the external ideal diodes respond quickly
nected from CLPROG to GND, the voltage on CLPROG
represents the input current:
whenever V
drops below BAT.
VCLPROG
RCLPROG
OUT
IVBUS = IBUSQ
+
•hCLPROG
If the load increases beyond the input current limit, ad-
ditional current will be pulled from the battery via the
ideal diodes. Furthermore, if power to V
where I
and h
are given in the Electrical
CLPROG
BUSQ
Characteristics.
(USB) or
BUS
V
(external wall power or high voltage regulator) is
OUT
removed, then all of the application power will be provided
35571fc
13
LTC3557/LTC3557-1
OPERATION
by the battery via the ideal diodes. The ideal diodes are
2. The WALL pin voltage falls below 3.2V.
fast enough to keep V
from dropping with just the
OUT
Each of these thresholds is suitably filtered in time to
prevent transient glitches on the WALL pin from falsely
triggering an event.
recommended output capacitor. The ideal diode consists
of a precision amplifier that enables an on-chip P-channel
MOSFET whenever the voltage at V
is approximately
OUT
SeetheApplicationsInformationsectionforanexplanation
of high voltage buck regulator control using the V pin.
15mV (V ) below the voltage at BAT. The resistance of
FWD
the internal ideal diode is approximately 200mΩ. If this is
sufficientfortheapplication,thennoexternalcomponents
are necessary. However, if more conductance is needed,
an external P-channel MOSFET can be added from BAT
C
Suspend Mode
When ILIM0 is pulled low and ILIM1 is pulled high the
LTC3557/LTC3557-1 enters Suspend mode to comply
with the USB specification. In this mode, the power path
to V
.
OUT
TheGATEpinoftheLTC3557/LTC3557-1drivesthegateof
the external P-channel MOSFET for automatic ideal diode
control. The source of the MOSFET should be connected
between V
and V
BUS
is put in a high impedance state to
BUS
reduce the V
OUT
input current to 50μA. If no other power
source is available to drive WALL and V , the system
OUT
to V
and the drain should be connected to BAT. Capable
OUT
loadconnectedtoV issuppliedthroughtheidealdiodes
OUT
of driving a 1nF load, the GATE pin can control an external
connectedtoBAT.IfanexternalpowersourcedrivesWALL
P-channel MOSFET having extremely low on-resistance.
and V
such that V
< V , the Suspend mode V
OUT BUS BUS
OUT
input current can be as high as 200μA.
Using the WALL Pin to Detect the Presence of an
External Power Source
3.3V Always-On Supply
The WALL input pin can be used to identify the presence
of an external power source (particularly one that is not
The LTC3557/LTC3557-1 includes an ultralow quiescent
currentlowdropoutregulatorthatisalwayspowered.This
LDOcanbeusedtoprovidepowertoasystempushbutton
controller or standby microcontroller. Designed to deliver
up to 25mA, the always-on LDO requires a 1μF MLCC
bypass capacitor for compensation. The LDO is powered
subject to a fixed current limit like the USB V
input).
BUS
Typically, such a power supply would be a 5V wall adapter
output or the low voltage output of a high voltage buck
regulator (specifically, LT3480, LT3481 or LT3505). When
the wall adapter output (or buck regulator output) is con-
nected directly to the WALL pin, and the voltage exceeds
from V , and therefore will enter dropout at loads less
OUT
than 25mA as V
not used, it should be disabled by connecting it to V
falls near 3.3V. If the LDO3V3 output is
OUT
the WALL pin threshold, the USB power path (from V
BUS
.
OUT
to V ) will be disconnected. Furthermore, the ACPR pin
OUT
will be pulled low. In order for the presence of an external
power supply to be acknowledged, both of the following
conditions must be satisfied:
V
Undervoltage Lockout (UVLO)
BUS
An internal undervoltage lockout circuit monitors V
and keeps the input current limit circuitry off until V
BUS
BUS
1. The WALL pin voltage must exceed approximately
4.3V.
rises above the rising UVLO threshold (3.8V) and at least
50mV above V . Hysteresis on the UVLO turns off the
OUT
2. The WALL pin voltage must exceed 75mV above the
BAT pin voltage.
inputcurrentlimitifV
dropsbelow3.7Vor50mVbelow
BUS
V
OUT
. When this happens, system power at V
will be
OUT
drawn from the battery via the ideal diode. To minimize the
possibility of oscillation in and out of UVLO when using
resistive input supplies, the input current limit is reduced
The input power path (between V
and V ) is
OUT
BUS
re-enabled and the ACPR pin is pulled high when either
of the following conditions is met:
as V
drops below 4.45V typical.
BUS
1. The WALL pin voltage falls to within 25mV of the BAT
pin voltage.
35571fc
14
LTC3557/LTC3557-1
OPERATION
Battery Charger
battery is always topped off, a charge cycle will automati-
cally begin when the battery voltage falls below V
RECHRG
TheLTC3557/LTC3557-1includesaconstantcurrent/con-
stant voltage battery charger with automatic recharge,
automatic termination by safety timer, low voltage trickle
charging, bad cell detection and thermistor sensor input
for out of temperature charge pausing.
(typically 4.1V for the LTC3557 or 4V for LTC3557-1). In
the event that the safety timer is running when the battery
voltage falls below V
, the timer will reset back to
RECHRG
zero. To prevent brief excursions below V
from re-
RECHRG
setting the safety timer, the battery voltage must be below
formorethan1.3ms. Thechargecycleandsafety
When a battery charge cycle begins, the battery charger
first determines if the battery is deeply discharged. If the
batteryvoltageisbelowV
V
RECHRG
timerwillalsorestartiftheV
UVLOcycleslowandthen
BUS
,typically2.85V,anautomatic
high (e.g., V , is removed and then replaced).
TRKL
BUS
trickle charge feature sets the battery charge current to
10% of the programmed value. If the low voltage persists
for more than 1/2 hour, the battery charger automatically
terminates and indicates via the CHRG pin that the battery
was unresponsive.
Charge Current
The charge current is programmed using a single resistor
from PROG to ground. 1/1000th of the battery charge
current is delivered to PROG which will attempt to servo
to1.000V. Thus, thebatterychargecurrentwilltrytoreach
1000 times the current in the PROG pin. The program
resistor and the charge current are calculated using the
following equations:
Oncethebatteryvoltageisabove2.85V,thebatterycharger
begins charging in full power constant current mode. The
current delivered to the battery will try to reach 1000V/
R
PROG
. Depending on available input power and external
load conditions, the battery charger may or may not be
able to charge at the full programmed rate. The external
load will always be prioritized over the battery charge
current. The USB current limit programming will always
be observed and only additional current will be available
to charge the battery. When system loads are light, battery
charge current will be maximized.
1000V
ICHG
1000V
RPROG
RPROG
=
, ICHG =
Ineithertheconstantcurrentorconstantvoltagecharging
modes, the PROG pin voltage will be proportional to the
actual charge current delivered to the battery. Therefore,
the actual charge current can be determined at any
time by monitoring the PROG pin voltage and using the
following equation:
Charge Termination
The battery charger has a built-in safety timer. When the
battery voltage approaches the float voltage (4.2V for
LTC3557or4.1VforLTC3557-1),thechargecurrentbegins
to decrease as the LTC3557/LTC3557-1 enters constant
voltage mode. Once the battery charger detects that it
has entered constant voltage mode, the four hour safety
timer is started. After the safety timer expires, charging
of the battery will terminate and no more current will be
delivered.
VPROG
RPROG
IBAT
=
•1000
In many cases, the actual battery charge current, I , will
BAT
belowerthanI
duetolimitedinputcurrentavailableand
CHG
prioritization with the system load drawn from V
.
OUT
Thermal Regulation
To prevent thermal damage to the IC or surrounding
components, an internal thermal feedback loop will
automatically decrease the programmed charge current
if the die temperature rises to approximately 110°C.
Thermal regulation protects the LTC3557/LTC3557-1
from excessive temperature due to high power operation
Automatic Recharge
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
35571fc
15
LTC3557/LTC3557-1
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
LTC3557/LTC3557-1 or external components. The benefit
of the LTC3557/LTC3557-1 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 conditions.
own unique “blink” rate for human recognition as well as
two unique duty cycles for machine recognition.
Table 2: illustrates the four possible states of the CHRG
pin when the battery charger is active.
Table 2: CHRG Output Pin
MODULATION
(BLINK)
STATUS
FREQUENCY
0Hz
FREQUENCY
DUTY CYCLE
100%
Charging
0Hz (Lo-Z)
I
< C/10
0Hz
0Hz (Hi-Z)
0%
BAT
Charge Status Indication
NTC Fault
Bad Battery
35kHz
35kHz
1.5Hz at 50%
6.1Hz at 50%
6.25% or 93.75%
12.5% or 87.5%
The CHRG pin indicates the status of the battery charger.
Four possible states are represented by CHRG which
include charging, not charging, unresponsive battery and
battery temperature out of range.
An NTC fault is represented by a 35kHz pulse train whose
duty cycle toggles 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.
The signal at the CHRG pin can be easily recognized as
one of the above four states by either a human or a mi-
croprocessor. An open-drain output, the CHRG pin can
drive an indicator LED through a current limiting resistor
for human interfacing or simply a pull-up resistor for
microprocessor interfacing.
Ifabatteryisfoundtobeunresponsivetocharging(i.e.,its
voltage remains below V
, typically 2.8V, for 1/2 hour),
TRKL
the CHRG pin gives the battery fault indication. For this
fault, a human would easily recognize the frantic 6.1Hz
“fast” blink 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. Note that the LTC3557/LTC3557-1 is
a 3-terminal PowerPath product where system load is
always prioritized over battery charging. Due to excessive
system load, there may not be sufficient power to charge
the battery beyond the trickle charge threshold voltage
within the bad battery timeout period. In this case, the
battery charger will falsely indicate a bad battery. System
software may then reduce the load and reset the battery
charger to try again.
To make the CHRG pin easily recognized by both humans
and microprocessors, the pin is either a DC signal of
ON for charging, OFF 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.
When charging begins, CHRG is pulled low and remains
low for the duration of a normal charge cycle. When charg-
ing is complete, i.e., the charger enters constant voltage
mode and the charge current has dropped to one-tenth
of the programmed value, the CHRG pin is released (high
impedance). The CHRG pin does not respond to the C/10
threshold if the LTC3557/LTC3557-1 is in input current
limit. This prevents false end of charge indications due to
insufficient power available to the battery charger. If a fault
occurs,thepinisswitchedat35kHz.Whileswitching,itsduty
cycle is modulated between a high 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
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.
35571fc
16
LTC3557/LTC3557-1
OPERATION
NTC Thermistor
AsingleMODEpinsetsallstep-downswitchingregulators
in Burst Mode or pulse-skip mode operation, while each
regulator is enabled individually through their respective
enable pins (EN1, EN2 and EN3). It is recommended that
Thebatterytemperatureismeasuredbyplacinganegative
temperature coefficient (NTC) thermistor close to the bat-
tery pack. The NTC circuitry is shown in Figure 8. To use
this feature connect the NTC thermistor, R , between
the NTC pin and ground and a bias resistor, R
thestep-downswitchingregulatorinputsupplies(V and
IN1
NTC
V
) be connected to the system supply pin (V ). This
IN2
OUT
, from
NOM
allows the undervoltage lock out circuit on the V
pin
OUT
V
to NTC. R
should be a 1% resistor with a value
NTC
NOM
(V UVLO)todisablethestep-downswitchingregulators
OUT
equal to the value of the chosen NTC thermistor at 25°C
(R25).A100kthermistorisrecommendedsincethermistor
current is not measured by the LTC3557/LTC3557-1 and
will have to be considered for USB compliance.
when the V
voltage drops below V
UVLO threshold.
OUT
OUT
Ifdrivingthestep-downswitchingregulatorinputsupplies
from a voltage other than V the regulators should
OUT
not be operated outside the specified operating range as
operation is not guaranteed beyond this range.
The LTC3557/LTC3557-1 will pause charging when the
resistance of the NTC thermistor drops to 0.54 times the
value of R25 or approximately 54k (for a Vishay “Curve 1”
thermistor,thiscorrespondstoapproximately40°C).Ifthe
battery charger is in constant voltage (float) mode, the
safety timer also pauses until the thermistor indicates a
return to a valid temperature. As the temperature drops,
the resistance of the NTC thermistor rises. The LTC3557/
LTC3557-1 is also designed to pause charging when the
valueoftheNTCthermistorincreasesto3.25timesthevalue
of R25. For a Vishay “Curve 1” thermistor this resistance,
325k, correspondstoapproximately0°C. Thehotandcold
comparators each have approximately 3°C of hysteresis
to prevent oscillation about the trip point. Grounding the
NTC pin disables all NTC functionality.
Step-Down Switching Regulator Output Voltage
Programming
Figure 2 shows the step-down switching regulator
application circuit. The full-scale output voltage for each
step-down switching regulator is programmed using a
resistor divider from the step-down switching regulator
output connected to the feedback pins (FB1, FB2 and
FB3) such that:
R1
R2
⎛
⎞
⎠
VOUTx = 0.8V •
+ 1
⎜
⎝
⎟
Typical values for R1 are in the range of 40k to 1M. The
capacitorC cancelsthepolecreatedbyfeedbackresistors
FB
General Purpose Step-Down Switching Regulators
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
TheLTC3557/LTC3557-1includesthree2.25MHzconstant
frequency current mode step-down switching regulators
providing400mA,400mAand600mAeach.Allstep-down
switching regulators can be programmed for a minimum
output voltage of 0.8V and can be used to power a micro-
controllercore,microcontrollerI/O,memoryorotherlogic
circuitry.Allstep-downswitchingregulatorssupport100%
duty cycle operation (low dropout mode) when the input
voltage drops very close to the output voltage and are also
capableofBurstModeoperationforhighestefficienciesat
light loads (Burst Mode operation is pin selectable). The
step-down switching regulators also include soft-start to
limitinrushcurrentwhenpoweringon,short-circuitcurrent
protection,andswitchnodeslewlimitingcircuitrytoreduce
EMI radiation. No external compensation components are
required for the switching regulators.
for C but a value of 10pF is recommended for most
FB
applications.Experimentationwithcapacitorsizesbetween
2pF and 22pF may yield improved transient response.
V
IN
EN
MP
L
SWx
FBx
PWM
CONTROL
V
OUTx
MODE
C
OUT
MN
C
R1
FB
0.8V
R2
GND
35571 F02
Figure 2. Buck Converter Application Circuit
35571fc
17
LTC3557/LTC3557-1
OPERATION
Step-Down Switching Regulator RST2 Operation
continuously. When operating continuously, regulation
and low noise output voltage are maintained, but input
operating current will increase to a few milliamps.
The RST2 pin is an open-drain output used to indicate that
step-down switching regulator 2 has been enabled and
has reached its final voltage. A 230ms delay is included
from the time switching regulator 2 reaches 92% of its
regulationvaluetoallowasystemcontrollerampletimeto
reset itself. RST2 may be used as a power-on reset to the
microprocessor powered by regulator 2 or may be used to
enable regulators 1 and/or 3 for supply sequencing. RST2
is an open-drain output and requires a pull-up resistor to
the output voltage of regulator 2 or another appropriate
power source.
In Burst Mode operation, the step-down switching regula-
tors automatically switch between fixed frequency PWM
operation and hysteretic control as a function of the load
current. At light loads the step-down switching regulators
control the inductor current directly and use a hysteretic
control loop to minimize both noise and switching losses.
WhileoperatinginBurstModeoperation,theoutputcapaci-
torischargedtoavoltageslightlyhigherthantheregulation
point. The step-down 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 powered down, helping conserve
battery power. When the output voltage drops below a
pre-determined value, the step-down switching regulator
circuitryispoweredonandanotherburstcyclebegins.The
sleeptimedecreasesastheloadcurrentincreases.Beyond
a certain load current point (about 1/4 rated output load
current) the step-down switching regulators 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.
Step-Down Switching Regulator Operating Modes
The step-down switching regulators include two possible
operating modes to meet the noise/power needs of a
variety of applications.
In pulse-skip mode, an internal latch is set at the start of
every cycle, which turns on the main P-channel MOSFET
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
internaltothestep-downswitchingregulatorrequiringonly
asingleceramicoutputcapacitorforstability.Atlightloads
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,
SW2 or SW3) goes high impedance and the switch node
voltage will “ring”. This is discontinuous operation, and is
normalbehaviorforaswitchingregulator.Atverylightloads
in pulse-skip mode, the step-down switching regulators
will automatically skip pulses as needed to maintain
Thestep-downswitchingregulatorsallowmodetransition
on-the-fly, providing seamless transition between modes
even 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.
Step-Down Switching Regulator in Shutdown
The step-down switching regulators are in shutdown
when not enabled for operation. In shutdown all circuitry
inthestep-downswitchingregulatorisdisconnectedfrom
the switching regulator input supply leaving only a few
nanoamps of leakage current. The step-down switching
regulatoroutputsareindividuallypulledtogroundthrough
a 10k resistor on the switch pin (SW1, SW2 or SW3) when
in shutdown.
output regulation. At high duty cycle (V
> V /2) it is
OUTX
INX
possible for the inductor current to reverse at light loads
causing the stepped down switching regulator to operate
35571fc
18
LTC3557/LTC3557-1
OPERATION
Step-down Switching Regulator Dropout Operation
outside the specified operating range as operation is not
guaranteed beyond this range.
It is possible for a step-down switching regulator’s input
voltagetoapproachitsprogrammedoutputvoltage(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.
Step-Down Switching Regulator Inductor Selection
Many different sizes and shapes of inductors are avail-
able from numerous manufacturers. Choosing the right
inductor from such a large selection of devices can be
overwhelming, but following a few basic guidelines will
make the selection process much simpler.
The step-down converters are designed to work with
inductors in the range of 2.2μH to 10μH. For most
applications a 4.7μH inductor is suggested for step-down
switching regulators providing up to 400mA of output
currentwhilea3.3μHinductorissuggestedforstep-down
switching regulators providing up to 600mA. Larger value
inductors reduce ripple current, which improves output
ripple voltage. Lower value inductors result in higher
ripple current and improved transient response time,
but will reduce the available output current. To maximize
efficiency, choose an inductor with a low DC resistance.
For a 1.2V output, efficiency is reduced about 2% for
100mΩ series resistance at 400mA load current, and
about 2% for 300mΩ series resistance at 100mA 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 step-down converters.
Step-Down Switching Regulator Soft-Start Operation
Soft-startisaccomplishedbygraduallyincreasingthepeak
inductor current for each step-down switching regulator
overa500ꢀsperiod.Thisallowseachoutputtoriseslowly,
helping minimize inrush current required to charge up the
switching regulator output capacitor. A soft-start cycle
occurs whenever a given switching regulator 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 transition
when actively changing between operating modes.
Step-Down Switching Regulator Switching
Slew Rate Control
The step-down switching regulators contain new patent-
pending circuitry to limit the slew rate of the switch node
(SW1, SW2 and SW3). This new circuitry is designed to
transition the switch node over a period of a couple nano-
seconds,significantlyreducingradiatedEMIandconducted
supply noise while maintaining high efficiency.
Differentcorematerialsandshapeswillchangethesize/cur-
rent and price/current relationship of an inductor. Toroid
or shielded pot cores in ferrite or Permalloy materials are
small 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
core and 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 step-down switching
regulators requires to operate.
Step-Down Switching Regulator Low Supply Operation
An undervoltage lockout (UVLO) circuit on V
shuts
OUT
downthestep-downswitchingregulatorswhenV drops
OUT
below about 2.7V. It is recommended that the step-down
switching regulators input supplies be connected to
the power path output (V ). This UVLO prevents the
OUT
step-down switching regulators’ from operating at low
supply voltages where loss of regulation or other un-
desirable operation may occur. If driving the step-down
switching regulator input supplies from a voltage other
than the V
pin, the regulators should not be operate
OUT
35571fc
19
LTC3557/LTC3557-1
OPERATION
The inductor value also has an effect on Burst Mode
operation. Lower inductor values will cause Burst Mode
switching frequency to increase.
switching regulator outputs. For good transient response
and stability the output capacitor for step-down switching
regulators should retain at least 4ꢀF of capacitance over
operating temperature and bias voltage. Each switching
regulator input supply should be bypassed with a 2.2ꢀF
capacitor. Consult with capacitor manufacturers for
detailed information on their selection and specifications
of ceramic capacitors. Many manufacturers now offer
very thin (<1mm tall) ceramic capacitors ideal for use in
height-restricted designs. Table 4 shows a list of several
ceramic capacitor manufacturers.
Table 3 shows several inductors that work well with the
step-down switching regulators. 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.
Step-Down Switching Regulator Input/Output
Capacitor Selection
Table 4. Ceramic Capacitor Manufacturers
LowESR(equivalentseriesresistance)ceramiccapacitors
should be used at both step-down switching regulator
outputs as well as at each step-down switching regulator
input supply. Only X5R or X7R ceramic capacitors should
be used because they retain their capacitance over wider
voltage and temperature ranges than other ceramic types.
A 10ꢀF output capacitor is sufficient for the step-down
AVX
www.avxcorp.com
www.murata.com
www.t-yuden.com
www.vishay.com
www.tdk.com
Murata
Taiyo Yuden
Vishay Siliconix
TDK
Table 3. Recommended Inductors for Step-Down Switching Regulators
SIZE in mm
(L × W × H)
INDUCTOR TYPE
L (μH)
MAX I (A)
MAX DCR (Ω)
MANUFACTURER
DC
DE2818C
4.7
3.3
1.25
1.45
0.072
0.053
Toko
www.toko.com
3.0 × 2.8 × 1.8
3.0 × 2.8 × 1.8
D312C
4.7
3.3
0.79
0.90
0.24
0.20
3.6 × 3.6 × 1.2
3.6 × 3.6 × 1.2
DE2812C
4.7
3.3
1.2
1.4
0.13*
0.105*
3.0 × 2.8 × 1.2
3.0 × 2.8 × 1.2
CDRH3D16
CDRH2D11
4.7
3.3
0.9
1.1
0.11
Sumida
www.sumida.com
4.0 × 4.0 × 1.8
4.0 × 4.0 × 1.8
3.2 × 3.2 × 1.2
3.2 × 3.2 × 1.2
0.085
4.7
3.3
0.5
0.6
0.17
0.123
CLS4D09
SD3118
4.7
0.75
0.19
4.9 × 4.9 × 1.0
4.7
3.3
1.3
1.59
0.162
0.113
Cooper
www.cooperet.com
3.1 × 3.1 × 1.8
3.1 × 3.1 × 1.8
SD3112
SD12
4.7
3.3
0.8
0.246
0.165
3.1 × 3.1 × 1.2
3.1 × 3.1 × 1.2
5.2 × 5.2 × 1.2
5.2 × 5.2 × 1.2
0.97
4.7
3.3
1.29
1.42
0.117*
0.104*
SD10
4.7
3.3
1.08
1.31
0.153*
0.108*
5.2 × 5.2 × 1.0
5.2 × 5.2 × 1.0
LPS3015
4.7
3.3
1.1
1.3
0.2
0.13
Coil Craft
www.coilcraft.com
3.0 × 3.0 × 1.5
3.0 × 3.0 × 1.5
*Typical DCR
35571fc
20
LTC3557/LTC3557-1
APPLICATIONS INFORMATION
External HV Buck Control Through the V Pin
compensation components are required on the V node.
C
C
The voltage at the V
pin is regulated to the larger of
OUT
The WALL, ACPR and V pins can be used in conjunction
C
(BAT + 300mV) or 3.6V as shown in Figures 6 and 7. The
feedback network of the high voltage regulator should be
settogenerateanoutputvoltagehigherthan4.4V(besure
to include the output voltage tolerance of the buck regula-
with an external high voltage buck regulator such as the
LT®3480, LT3481 or LT3505 to provide power directly
to the V
pin through a power P-channel MOSFET as
OUT
shown in Figures 3-5 (consult the factory for a complete
list of approved high voltage buck regulators). When the
tor). The V control of the LTC3557 overdrives the local
C
V control of the external high voltage buck. Therefore,
C
WALL pin voltage exceeds 4.3V, V pin control circuitry
C
once the V control is enabled, the output voltage is set
C
is enabled and drives the V pin of the LT3480, LT3481 or
C
independent of the buck regulator feedback network.
LT3505. The V pin control circuitry is designed so that no
C
HV
IN
4
2
3
8V TO 38V
(TRANSIENTS
TO 60V)
V
BOOST
LT3480
IN
0.47μF
6.8μH
68nF
150k
4.7μF
5
RUN/SS SW
R
T
10
DFLS240L
499k
40.2k
22μF
1
8
7
6
NC
NC
BD
FB
100k
GND
V
C
11
9
LT3480
Si2333DS
UP TO
2A
HIGH VOLTAGE
BUCK CIRCUITRY
V
OUT
26
3
25
C
OUT
V
WALL ACPR
C
23
21
22
V
OUT
GATE
BAT
LTC3557
LTC3557-1
Si2333DS
(OPT)
BAT
+
Li-Ion
35571 F03
Figure 3. LT3480 Buck Control Using VC (800kHz Switching)
4
2
HV
IN
8V TO 34V
V
BOOST
LT3481
RUN/SS SW
IN
0.47μF
68nF
150k
4.7μF
6.8μH
5
3
7
10
DFLS240L
R
BIAS
549k
200k
T
60.4k
22μF
1
8
BD
FB
C
6
NC
GND
11
V
9
LT3481
Si2333DS
UP TO
2A
HIGH VOLTAGE
BUCK CIRCUITRY
V
OUT
26
3
25
C
OUT
V
WALL ACPR
C
23
V
OUT
LTC3557
LTC3557-1
21
Si2333DS
(OPT)
GATE
22
BAT
BAT
+
Li-Ion
35571 F04
Figure 4. LT3481 Buck Control Using VC (800kHz Switching)
35571fc
21
LTC3557/LTC3557-1
APPLICATIONS INFORMATION
1N4148
3
1
2
HV
IN
V
BOOST
SW
IN
8V TO 36V
0.1μF
68nF
20k
150k
1μF
LT3505
6.8μH
4
SHDN
49.9k
10.0k
BZT52C16T
MBRM140
10μF
806k
6
R
7
T
FB
C
GND
5, 9
V
8
LT3505
Si2333DS
UP TO
1.2A
HIGH VOLTAGE
BUCK CIRCUITRY
V
OUT
26
3
25
C
OUT
V
WALL ACPR
C
23
21
22
V
OUT
GATE
BAT
LTC3557
LTC3557-1
Si2333DS
(OPT)
BAT
+
Li-Ion
35571 F05
Figure 5. LT3505 Buck Control Using VC (2.2MHz Switching with Frequency Foldback)
5.0
4.5
4.0
3.5
3.0
2.5
This technique provides a significant efficiency advantage
over the use of a 5V buck to drive the battery charger. With
a simple 5V buck output driving V , battery charger
OUT
efficiency is approximately:
VBAT
5V
ηCHARGER = ηBUCK
•
I
I
I
= 0.0A
= 0.75A
= 1.5A
O
O
O
where η
is the efficiency of the high voltage buck
BUCK
regulatorand5Vistheoutputvoltageofthebuckregulator.
With a typical buck efficiency of 87% and a typical battery
voltage of 3.8V, the total battery charger efficiency is
approximately 66%. Assuming a 1A charge current, this
works out to nearly 2W of power dissipation just to charge
the battery!
BAT
3.5
4
2.5
3
4.5
35571 F06
BAT (V)
Figure 6. LTC3557 VOUT Voltage vs Battery Voltage
with the LT3480
5.0
4.5
4.0
3.5
3.0
With the V control technique, battery charger efficiency
C
is approximately:
VBAT
0.3V + VBAT
ηCHARGER = ηBUCK
•
With the same assumptions as above, the total battery
charger efficiency is approximately 81%. This example
works out to just 900mW of power dissipation. For
applications, component selection and board layout
information beyond those listed here please refer to the
respective LT3480, LT3481 or LT3505 data sheet.
I
I
= 0.0A
= 0.6A
O
O
BAT
2.5
2.5
3
3.5
4
4.5
35571 F07
BAT (V)
Figure 7. LTC3557-1VOUT Voltage vs Battery Voltage
with the LT3505
35571fc
22
LTC3557/LTC3557-1
APPLICATIONS INFORMATION
Alternate NTC Thermistors and Biasing
for the hot threshold and 0.765 • V
for the cold
VNTC
threshold.
The LTC3557/LTC3557-1 provides temperature qualified
charging if a grounded thermistor and a bias resistor
are connected to NTC. 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,
respectively (assuming a Vishay “Curve 1” thermistor).
Therefore, the hot trip point is set when:
RNTC|HOT
• VVNTC = 0.349 • VVNTC
RNOM +RNTC|HOT
and the cold trip point is set when:
RNTC|COLD
The upper and lower temperature thresholds can be
adjusted 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 adjustment resistor, both the upper and the lower
temperaturetrippointscanbeindependentlyprogrammed
withtheconstraintthatthedifferencebetweentheupperand
lower temperature thresholds cannot decrease. Examples
of each technique are given below.
• VVNTC = 0.765 • VVNTC
RNOM +RNTC|COLD
SolvingtheseequationsforR
in the following:
andR
results
NTC|COLD
NTC|HOT
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 non-linear 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
R
= Value of thermistor at the cold trip point
= Value of the thermistor at the hot trip
NTC|COLD
rHOT
0.536
NTC|HOT
point
RNOM
=
=
•R25
rCOLD
3.25
r
r
= Ratio of R
to R25
COLD
NTC|COLD
RNOM
•R25
= Ratio of R
to R25
HOT
NTC|HOT
where r
and r
are the resistance ratios at the
R
NOM
= Primary thermistor bias resistor (see Figure 8)
HOT
COLD
desired hotandcoldtrippoints.Notethattheseequations
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.
R1 = Optional temperature range adjustment resistor
(see Figure 9)
The trip points for the LTC3557/LTC3557-1’s temperature
qualification are internally programmed at 0.349 • V
VNTC
35571fc
23
LTC3557/LTC3557-1
APPLICATIONS INFORMATION
From the Vishay Curve 1 R-T characteristics, r
is
the nearest 1% value is 12.7k. The final solution is shown
in Figure 9 and results in an upper trip point of 45°C and
a lower trip point of 0°C.
HOT
0.2488 at 60°C. Using the above equation, R
should
NOM
, the cold trip
be set to 46.4k. With this value of R
NOM
point is about 16°C. Notice that the span is now 44°C
rather than the previous 40°C. This is due to the decrease
in “temperature gain” of the thermistor as absolute
temperature increases.
Battery Charger Stability Considerations
TheLTC3557/LTC3557-1’sbatterychargercontainsbotha
constant voltage and a constant current control loop. The
constant voltage loop is stable without any compensation
when a battery is connected with low impedance leads.
Excessive lead length, however, may add enough series
inductancetorequireabypasscapacitorofatleast1μFfrom
BAT to GND. Furthermore, a 4.7μF capacitor in series with
a 0.2Ω to 1Ω resistor from BAT to GND is required to keep
ripple voltage low when the battery is disconnected.
The upper and lower temperature trip points can be
independently programmed by using an additional bias
resistor as shown in Figure 9. The following formulas can
be used to compute the values of R
and R1:
NOM
rCOLD –rHOT
RNOM
=
•R25
2.714
R1= 0.536 •RNOM –rHOT •R25
High value, low ESR multilayer ceramic chip capacitors
reduce the constant voltage loop phase margin, possibly
resulting in instability. Ceramic capacitors up to 22μF may
beusedinparallelwithabattery,butlargerceramicsshould
be decoupled with 0.2Ω to 1Ω of series resistance.
For example, to set the trip points to 0°C and 45°C with
a Vishay Curve 1 thermistor choose
3.266 – 0.4368
RNOM
=
• 100k = 104.2k
In constant current mode, the PROG pin is in the feedback
loop rather than the battery voltage. Because of the
additional pole created by any PROG pin capacitance,
capacitance on this pin must be kept to a minimum. With
2.714
the nearest 1% value is 105k.
R1 = 0.536 • 105k – 0.4368 • 100k = 12.6k
V
V
NTC
NTC
NTC BLOCK
NTC BLOCK
18
18
0.765 • V
0.765 • V
VNTC
VNTC
R
R
NOM
NOM
–
+
–
+
100k
105k
TOO_COLD
TOO_HOT
TOO_COLD
TOO_HOT
NTC
NTC
19
19
R
100k
R1
12.7k
NTC
–
+
–
+
0.349 • V
0.349 • V
VNTC
VNTC
R
NTC
100k
+
–
+
–
NTC_ENABLE
NTC_ENABLE
0.017 • V
0.017 • V
VNTC
VNTC
35571 F08
35571 F09
Figure 8. Typical NTC Thermistor Circuit
Figure 9. NTC Thermistor Circuit with Additional Bias Resistor
35571fc
24
LTC3557/LTC3557-1
APPLICATIONS INFORMATION
It is not necessary to perform any worst-case power
dissipation scenarios because the LTC3557/LTC3557-1
will automatically reduce the charge current to maintain
the die temperature at approximately 110°C. However, the
approximate ambient temperature at which the thermal
feedback begins to protect the IC is:
no additional capacitance on the PROG pin, the battery
charger is stable with program resistor values as high
as 25k. However, additional capacitance on this node
reduces the maximum allowed program resistor. The pole
frequency at the PROG pin should be kept above 100kHz.
Therefore, if the PROG pin has a parasitic capacitance,
C
, the following equation should be used to calculate
PROG
T = 110°C – P • θ
JA
A
D
the maximum resistance value for R
:
PROG
Example: Consider the LTC3557/LTC3557-1 operating
from a wall adapter with 5V (V ) providing 1A (I
1
)
BAT
OUT
RPROG
≤
2π • 100kHz • CPROG
to charge a Li-Ion battery at 3.3V (BAT). Also assume
= P = P = 0.05W, so the total power
P
D(SW1)
dissipation is:
D(SW2)
D(SW3)
Printed Circuit Board Power Dissipation
Considerations
P = (5V – 3.3V) • 1A + 0.15W = 1.85W
D
In order to be able to deliver maximum charge current
under all conditions, it is critical that the Exposed Pad on
thebacksideoftheLTC3557/LTC3557-1packageissoldered
to a ground plane on the board. Correctly soldered to a
The ambient temperature above which the LTC3557/
LTC3557-1 will begin to reduce the 1A charge current, is
approximately:
2
T = 110°C – 1.85W • 37°C/W = 42°C
A
2500mm ground plane on a double-sided 1oz copper
board, the LTC3557/LTC3557-1 has a thermal resistance
The LTC3557/LTC3557-1 can be used above 42°C, but the
chargecurrentwillbereducedbelow1A.Thechargecurrent
at a given ambient temperature can be approximated by:
(θ ) of approximately 37°C/W. Failure to make good
JA
thermal contact between the Exposed Pad on the backside
of the package and an adequately sized ground plane will
result in thermal resistances far greater than 37°C/W.
110°C – TA
PD =
θJA
The conditions that cause the LTC3557/LTC3557-1 to
reduce charge current due to the thermal protection
feedback can be approximated by considering the power
dissipated in the part. For high charge currents and a wall
= V
(
– BAT •IBAT +PD(SW1) +PD(SW2) +PD(SW3)
)
OUT
thus:
adapter applied to V , the LTC3557/LTC3557-1 power
OUT
dissipation is approximately:
110°C – TA
−PD(SW1) –PD(SW2) –PD(SW3)
θJA
P = (V
– BAT) • I + P
+ P
+ P
D
OUT
BAT
D(SW1)
D(SW2) D(SW3)
IBAT
=
VOUT – BAT
where, P is the total power dissipated, V
is the supply
D
OUT
voltage, BAT is the battery voltage and I is the battery
BAT
Consider the above example with an ambient temperature of
55°C. The charge current will be reduced to approximately:
chargecurrent.P
isthepowerlossbythestep-down
switching regulators. The power loss for a step-down
D(SWx)
110°C – 55°C
− 0.15W
switching regulator can be calculated as follows:
37°C/W
P
= (OUTx • I ) • (100 – Eff)/100
OUT
D(SWx)
IBAT
=
=
5V – 3.3V
where OUTx is the programmed output voltage, I
is
OUT
1.49W – 0.15W
1.7V
the load current and Eff is the % efficiency which can be
measured or looked up on an efficiency graph for the
programmed output voltage.
= 786mA
35571fc
25
LTC3557/LTC3557-1
APPLICATIONS INFORMATION
If an external buck switching regulator controlled by the
3. The switching power traces connecting SW1, SW2 and
SW3 to their respective inductors should be minimized
to reduce radiated EMI and parasitic coupling. Due to
thelargevoltageswingoftheswitchingnodes,sensitive
nodes such as the feedback nodes (FB1, FB2 and FB3)
should be kept far away or shielded from the switching
nodes or poor performance could result.
LTC3557/LTC3557-1 V pin is used instead of a 5V wall
C
adapter we see a significant reduction in power dissipated
by the LTC3557/LTC3557-1. This is because the external
buck switching regulator will drive the PowerPath output
(V ) to about 3.6V with the battery at 3.3V. If you go
OUT
through the example above and substitute 3.6V for V
OUT
we see that thermal regulation does not kick in until about
93°C. Thus, the external regulator not only allows higher
charging currents, but lower power dissipation means a
cooler running application.
4. Connectionsbetweenthestep-downswitchingregulator
inductorsandtheirrespectiveoutputcapacitorsshould
bekeptasshortaspossible. TheGNDsideoftheoutput
capacitorsshouldconnectdirectlytothethermalground
plane of the part.
Printed Circuit Board Layout Considerations
5. Keep the feedback pin traces (FB1, FB2 and FB3) as
short as possible. Minimize any parasitic capacitance
between the feedback traces and any switching node
(i.e., SW1, SW2, SW3 and logic signals). If necessary
shield the feedback nodes with a GND trace
When laying out the printed circuit board, the following
list should be followed to ensure proper operation of the
LTC3557/LTC3557-1:
1. TheExposedPadofthepackage(Pin29)shouldconnect
directlytoalargegroundplanetominimizethermaland
electrical impedance.
6) Connections between the LTC3557/LTC3557-1
power path pins (V
and V ) and their respective
BUS
OUT
2. Thetraceconnectingthestep-downswitchingregulator
input supply pins (V and V ) and their respective
decoupling capacitors should be kept as short as pos-
sible. The GND side of these capacitors should connect
directly to the ground plane of the part. V
IN1
IN2
decoupling capacitors should be kept as short as
possible. The GND side of these capacitors should
connect directly to the ground plane of the part. These
capacitors provide the AC current to the internal power
MOSFETs and their drivers. It’s important to minimize
inductance from these capacitors to the pins of the
should be
OUT
decoupled with a 10μF or greater ceramic capacitor as
close as possible to the LTC3557/LTC3557-1.
LTC3557/LTC3557-1. Connect V and V to V
IN1
IN2
OUT
through a short low impedance trace.
35571fc
26
LTC3557/LTC3557-1
TYPICAL APPLICATION
HV
IN
OPTIONAL HIGH VOLTAGE
4
5
2
3
8V TO 38V
(TRANSIENTS
TO 60V)
V
BOOST
SW
BUCK INPUT
IN
0.47μF
68nF
150k
4.7μF
LT3480
6.8μH
RUN/SS
10
R
DFLS240L
T
499k
40.2k
22μF
6
7
1
8
NC
NC
SYNC
PG
BD
FB
100k
GND
V
C
11
9
Si2333DS
26
3
25
V
OUT
10μF
V
WALL ACPR
C
USB OR
5V WALL
ADAPTER
24
23
6
V
BUS
V
OUT
2.2μF
10μF
510Ω
BV
IN1
IN2
2.2μF
2.1k
2k
16
27
20
CLPROG BV
28
21
22
4
PROG
CHRG
GATE
Si2333DS
(OPT)
100k
18
19
BAT
V
NTC
BAT
3.3V
+
100k
NTC
Li-Ion
25mA
LDO3V3
NTC
ALWAYS ON
1μF
LTC3557/
LTC3557-1
3.3μH
4.7μH
V
OUT1
5
1
2
SW1
3.3V
ILIM0
600mA
10pF 1.02M
10pF 806k
10μF
10μF
ILIM1
EN1
324k
649k
7
9
FB1
PMIC
CONTROL
10
11
8
EN2
V
OUT3
17
SW3
1.8V
EN3
400mA
MODE
12
14
FB3
RST2
RST2
100k
4.7μH
V
OUT2
15
13
SW2
FB2
1.2V
400mA
10pF 232k
10μF
464k
GND
29
35571 TA02
35571fc
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.
27
LTC3557/LTC3557-1
PACKAGE DESCRIPTION
UF Package
28-Lead Plastic QFN (4mm × 4mm)
(Reference LTC DWG # 05-08-1721 Rev A)
PIN 1 NOTCH
R = 0.20 TYP
OR 0.35 s 45o
CHAMFER
BOTTOM VIEW—EXPOSED PAD
R = 0.115
0.75 p 0.05
4.00 p 0.10
TYP
(4 SIDES)
R = 0.05
TYP
27 28
0.70 p 0.05
0.40 p 0.05
PIN 1
TOP MARK
(NOTE 6)
1
2
2.64 p 0.10
(4-SIDES)
PACKAGE
OUTLINE
0.20 p 0.05
0.40 BSC
(UF28) QFN 0106 REVA
0.200 REF
0.20 p 0.05
0.40 BSC
0.00 – 0.05
DED SOLDER PAD PITCH AND DIMENSIONS
R MASK TO AREAS THAT ARE NOT SOLDERED
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, IF PRESENT
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
S NOT A JEDEC PACKAGE OUTLINE
NOT TO SCALE
SIONS ARE IN MILLIMETERS
RELATED PARTS
PART NUMBER
Power Management
LTC3455
DESCRIPTION
COMMENTS
Dual DC/DC Converter with USB Power Management and Efficiency >96%, Accurate USB Current Limiting (500mA/100mA),
Li-Ion Battery Charger
4mm × 4mm 24-Pin QFN Package
LTC3456
LTC3555
2-Cell Multi-Output DC/DC Converter with USB Power
Manager
Seamless Transition Between 2-Cell Battery, USB and AC Wall Adapter
Input Power Sources, QFN Package
Switching USB Power Manager with Li-Ion/Polymer
Charger, Triple Synchronous Buck Converter + LDO
Complete Multifunction PMIC: Switch Mode Power Manager and Three
Buck Regulators + LDO, Charge Current Programmable up to 1.5A from
Wall Adapter Input, Thermal Regulation Synchronous Buck Converters
Efficiency: >95%, ADJ Outputs: 0.8V to 3.6V at 400mA/400mA/1A
Bat-Track Adaptive Output Control, 200mΩ Ideal Diode, 4mm × 5mm
28-Pin QFN Package
LTC3559
Linear USB Li-Ion/Polymer Battery Charger with Dual
Synchronous Buck Converter
Adjustable Synchronous Buck Converters, Efficiency: >90%, Outputs:
Down to 0.8V at 400mA for each, Charge Current Programmable up to
950mA, USB Compatible, 3mm × 3mm 16-Pin QFN Package
Battery Chargers
LTC4055
USB Power Controller and Battery Charger
Charges Single Cell Li-Ion Batteries Directly from a USB Port, Thermal
Regulation, 200mΩ Ideal Diode, 4mm × 4mm 16-Pin QFN Package
LTC4066
LTC4085
USB Power Controller and Li-Ion Battery Charger with
Low Loss Ideal Diode
Charges Single Cell Li-Ion Batteries Directly from a USB Port, Thermal
Regulation, 50mΩ Ideal Diode, 4mm × 4mm 24-Pin QFN Package
USB Power Manager with Ideal Diode Controller and
Li-Ion Charger
Charges Single Cell Li-Ion Batteries Directly from a USB Port, Thermal
Regulation, 200mΩ Ideal Diode with <50mΩ Option, 4mm × 3mm
14-Pin DFN Package
LTC4088
High Efficiency USB Power Manager and Battery Charger Maximizes Available Power from USB Port, Bat-Track, “Instant On”
Operation, 1.5A Max Charge Current, 180mΩ Ideal Diode with <50mΩ
Option, 3.3V/25mA Always On LDO, 4mm × 3mm 14-Pin DFN Package
LTC4089/LTC4089-5 USB Power Manager with Ideal Diode Controller and
High Efficiency Li-Ion Battery Charger
1.2A Charger, 6V to 36V (40V
), 200mΩ Ideal Diode with 50mΩ
MAX
Option, 6mm × 3mm 22-Pin DFN Package
35571fc
LT 0808 REV C • PRINTED IN USA
LinearTechnology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
28
●
●
© LINEAR TECHNOLOGY CORPORATION 2007
(408) 432-1900 FAX: (408) 434-0507 www.linear.com
相关型号:
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