LT3502EDC_技术文档

LT3502/LT3502A

1.1MHz/2.2MHz, 500mA

Step-Down Regulators in

2mm × 2mm DFN

FEATURES

DESCRIPTION

The LT^®3502/LT3502A are current mode PWM step-down

DC/DC converters with an internal 500mA power switch,

in a tiny 8-lead 2mm × 2mm DFN package. The wide input

voltage range of 3V to 40V makes the LT3502/LT3502A

suitableforregulatingpowerfromawidevarietyofsources,

including24Vindustrialsuppliesandautomotivebatteries.

Its high operating frequency allows the use of tiny, low

cost inductors and capacitors, resulting in a very small

solution. Constant frequency above the AM band avoids

interfering with radio reception, making the LT3502A

particularly suitable for automotive applications.

■

3V to 40V Input Voltage Range

■

500mA Output Current

■

Switching Frequency: 2.2MHz (LT3502A),

1.1MHz (LT3502)

800mV Feedback Voltage

Short-Circuit Robust

Soft-Start

Low Shutdown Current: <2μA

Internally Compensated

Internal Boost Diode

■

Thermally Enhanced 2mm × 2mm 8-Lead DFN

Cycle-by-cycle current limit and frequency foldback pro-

vide protection against shorted outputs. Soft-start and

frequency foldback eliminates input current surge during

start-up. DA current sense provides further protection in

fault conditions. An internal boost diode reduces com-

ponent count.

APPLICATIONS

■

Automotive Systems

■

Battery-Powered Equipment

■

Wall Transformer Regulation

■

Distributed Supply Regulation

, LT, LTC and LTM are registered trademarks of Linear Technology Corporation.

All other trademarks are the property of their respective owners.

TYPICAL APPLICATION

3.3V Step-Down Converter

LT3502A 12V_INEfﬁciency

90

80

BD

V

IN

5V

3.3V

OUT

V

BOOST

SW

OUT

IN

4.7V TO 40V

70

60

50

40

30

20

10

1μF

0.1μF

6.8μH

V

OUT

3.3V

500mA

LT3502A

DA

FB

31.6k

SHDN

OFF ON

GND

10k

10μF

3502TA01a

0

0.4

0.5

0.1

0.2

0.3

LOAD CURRENT (A)

3502 TA01b

3502f

1

LT3502/LT3502A

PACKAGE/ORDER INFORMATION

ABSOLUTE MAXIMUM RATINGS

(Note 1)

Input Voltage (V )....................................................40V

TOP VIEW

IN

BOOST Voltage .........................................................50V

BOOST Pin Above SW Pin...........................................7V

FB Voltage...................................................................6V

SHDN Voltage ...........................................................40V

BD Voltage ..................................................................7V

Operating Junction Temperature Range (Note 2)

LT3502AE, LT3502E........................... –40°C to 125°C

LT3502AI, LT3502I ............................ –40°C to 125°C

Storage Temperature Range................... –65°C to 150°C

1

2

3

4

8

7

6

5

SW

V

IN

BD

FB

BOOST

DA

9

⎯

SHDN

GND

DC PACKAGE

8-LEAD (2mm × 2mm) PLASTIC DFN

θ

JA

= 102°C/W

EXPOSED PAD (PIN 9) IS GND, MUST BE SOLDERED TO PCB

ORDER PART NUMBER

DC PART MARKING*

LCLV

LT3502EDC

LT3502IDC

LCLV

LCLT

LT3502AEDC

LT3502AIDC

Order Options Tape and Reel: Add #TR

Lead Free: Add #PBF Lead Free Tape and Reel: Add #TRPBF

Lead Free Part Marking: http://www.linear.com/leadfree/

ConsultLTCMarketingforpartsspeciﬁedwithwideroperatingtemperatureranges.

*Thetemperaturegradeisidentiﬁedbyalabelontheshippingcontainer.

ELECTRICAL CHARACTERISTICS ^The● denotes the speciﬁcations which apply over the full operating

temperature range, otherwise speciﬁcations are at T_A= 25°C. V_IN= 10V, V_SHDN= 5V, V_BOOST= 15V.

⎯ ⎯ ⎯ ⎯

PARAMETER

CONDITIONS

MIN

TYP

2.8

0.5

1.5

MAX

UNITS

V

Undervoltage Lockout

Quiescent Current at Shutdown

Quiescent Current

2.6

3

2

V = 0V

⎯ ⎯ ⎯ ⎯

SHDN

μA

Not Switching

mA

●

Feedback Voltage

0.785

0.79

0.8

0.813

0.81

V

Reference Voltage Line Regulation

FB Pin Bias Current

0.005

15

%/V

nA

(Note 5)

50

Switching Frequency

I

< 500mA (LT3502A)

< 500mA (LT3502)

1.9

1.8

0.9

0.8

2.25

1.1

2.7

2.8

1.3

1.4

MHz

DA

●

1.1

Maximum Duty Cycle

100mA Load (LT3502A)

100mA Load (LT3502)

70

80

90

%

Switch V

I

= 500mA

SW

450

0.9

mV

A

CESAT

Switch Current Limit

Switch Active Current

(Note 3)

0.75

1.1

SW = 10V (Note 4)

SW = 0V (Note 5)

95

8

130

30

μA

BOOST Pin Current

I

= 500mA

= 100mA

10

1.9

0.8

650

13

2.2

1

mA

V

SW

OUT

Minimum BOOST Voltage Above Switch

BOOST Schottky Forward Drop

DA Pin Current to Stop OSC

V

500

mA

3502f

2

LT3502/LT3502A

ELECTRICAL CHARACTERISTICS ^The● denotes the speciﬁcations which apply over the full operating

temperature range, otherwise speciﬁcations are at T_A= 25°C. V_IN= 10V, V_SHDN= 5V, V_BOOST= 15V.

⎯ ⎯ ⎯ ⎯

PARAMETER

⎯ ⎯ ⎯ ⎯

CONDITIONS

MIN

TYP

MAX

UNITS

SHDN Bias Current

V

= 5V

= 0V

55

80

1

μA

⎯ ⎯ ⎯ ⎯

SHDN

V

SHDN

⎯

⎯ ⎯ ⎯ ⎯

SHDN Input Voltage High

⎯ ⎯ ⎯ ⎯

2

V

SHDN Input Voltage Low

0.3

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.

with statistical process controls. The LT3502IDC and LT3502AIDC are

guaranteed over the – 40°C to 125°C operating junction temperature

range.

Note 3: Current limit guaranteed by design and/or correlation to static test.

Note 2. The LT3502EDC and LT3502AEDC are guaranteed to meet

performance speciﬁcations from 0°C to 125°C junction temperature

range. Speciﬁcations over the –40°C to 125°C operating junction

temperature range are assured by design, characterization and correlation

Slope compensation reduces current limit at higher duty cycle.

Note 4: Current ﬂows into pin.

Note 5: Current ﬂows out of pin.

TYPICAL PERFORMANCE CHARACTERISTICS ^(T_A^{= 25°C unless otherwise noted)}

LT3502A 3.3V_OUTEfﬁciency

LT3502A 5V_OUTEfﬁciency

LT3502 3.3V_OUTEfﬁciency

90

80

70

60

50

40

30

20

10

90

80

70

60

50

40

30

20

10

100

90

80

70

60

50

40

30

20

10

0

12V

IN

5V

IN

24V

IN

12V

IN

24V

IN

12V

IN

0

0.4

0.5

0

0.1

0.3

LOAD CURRENT (A)

0.4

0.5

0.1

0.2

0.3

0.2

0

0.4

0.5

0.1

0.2

0.3

LOAD CURRENT (A)

3502 G02

3502 G03

3502 G01

LT3502A Maximum Load Current

V_OUT= 3.3V, L = 6.8μH

LT3502A Maximum Load Current

V_OUT= 5V, L = 10μH

LT3502 5V_OUTEfﬁciency

1.0

0.9

0.8

0.7

0.6

0.5

0.4

0.3

0.2

0.1

0

1.0

0.9

0.8

0.7

0.6

0.5

0.4

0.3

0.2

0.1

0

100

90

80

70

60

50

40

30

20

10

0

12V

IN

TYPICAL

24V

IN

MINIMUM

0

0.1

0.2

0.3

0.4

0.5

0

20

(V)

30

0

20

(V)

30

10

40

10

40

V

LOAD CURRENT (A)

IN

3502 G04

3502 G05

3502 G06

3502f

3

LT3502/LT3502A

TYPICAL PERFORMANCE CHARACTERISTICS ^(T_A^{= 25°C unless otherwise noted)}

LT3502 Maximum Load Current

V_OUT= 5V, L = 22μH

LT3502 Maximum Load Current

V_OUT= 3.3V, L = 15μH

Switch Voltage Drop

0.9

0.8

0.7

0.6

0.5

0.4

0.3

0.2

0.1

0

0.9

0.8

0.7

0.6

0.5

0.4

0.3

0.2

0.1

0

700

600

TYPICAL

MINIMUM

500

400

300

200

100

0

–40°C

25°C

125°C

20

(V)

0

10

30

40

20

(V)

0

10

30

40

0.2

0.4

0.6

1.0

0

0.8

V

SWITCH CURRENT (A)

IN

3502 G07

3502 G08

3502 G09

⎯ ⎯ ⎯ ⎯

Soft-Start (SHDN)

UVLO

Switching Frequency

0.9

0.8

0.7

0.6

0.5

0.4

0.3

0.2

0.1

0

3.5

3.0

2.5

2.0

1.5

1.0

0.5

0

LT3502A

2.0

1.5

1.0

0.5

0

LT3502

–0.1

1400

1600

0

50

150

0

200 400 600 800 1000 1200

SHDN PIN VOLTAGE (mV)

–50

100

0

50

100

–50

150

TEMPERATURE (°C)

3502 G12

3502 G10

3502 G11

⎯ ⎯ ⎯ ⎯

SHDN Pin Current

Switch Current Limit

1.0

0.9

0.8

0.7

0.6

0.5

0.4

0.3

0.2

0.1

0

300

250

1.2

1.0

SW PEAK CURRENT LIMIT

LT3502

LT3502A

200

0.8

0.6

DA VALLEY CURRENT LIMIT

150

100

0.4

0.2

0

50

0

–50

0

50

100

150

0

5

10 15 20 25 30 35 40 45

SHDN PIN VOLTAGE (V)

0

50

DUTY CYCLE (%)

100

TEMPERATURE (°C)

3502 G14

3502 G13

3502 G18

3502f

4

LT3502/LT3502A

TYPICAL PERFORMANCE CHARACTERISTICS ^(T_A^{= 25°C unless otherwise noted)}

LT3502A Maximum V_INfor Full

Frequency (V_OUT= 3.3V)

LT3502A Maximum V_INfor Full

Frequency (V_OUT= 5V)

LT3502 Maximum V_INfor Full

Frequency (V_OUT= 3.3V)

45

40

35

30

25

20

15

10

5

45

40

35

30

25

20

15

10

5

45

40

35

30

25

20

15

10

5

T

= 25°C

= 85°C

A

T

= 25°C

T = 25°C

A

T

= 85°C

T = 85°C

A

0

0.1 0.2 0.3

LOAD CURRENT (A)

0.7

0

0.1 0.2 0.3

LOAD CURRENT (A)

0.7

0.4 0.5 0.6

0

0.1 0.2 0.3

LOAD CURRENT (A)

0.7

0.4 0.5 0.6

3502 G16

3502 G17

3502 G15

LT3502A Typical Minimum Input

Voltage (V_OUT= 3.3V)

LT3502A Typical Minimum Input

Voltage (V_OUT= 5V)

LT3502 Typical Minimum Input

Voltage (V_OUT= 3.3V)

7

8

7

6

5

4

3

2

1

0

6

5

4

3

2

1

6

5

4

3

2

1

0

0.1

0.01

LOAD CURRENT (A)

1

0.1

0.01

LOAD CURRENT (A)

1

0.001

0.01

0.1

1

LOAD CURRENT (A)

3502 G20

3502 G19

3502 G21

LT3502 Typical Minimum Input

Voltage (V_OUT= 5V)

Continuous Mode Waveform

Discontinuous Mode Waveform

8

7

6

5

4

3

2

1

0

V

SW

5V/DIV

I

L

200mA/DIV

I

L

200mA/DIV

V

OUT

V

OUT

20mV/DIV

3502 G23

3502 G24

V

= 12V

200ns/DIV

V

= 12V

200ns/DIV

IN

OUT

IN

OUT

= 3.3V

L = 6.8μH

C

I

= 10μF

OUT

= 250mA

C

I

= 10μF

OUT

= 30mA

0.001

0.01

0.1

1

OUT

LOAD CURRENT (A)

3502 G22

3502f

5

LT3502/LT3502A

PIN FUNCTIONS

V (Pin 1): The V pin supplies current to the LT3502/

GND (Pin 5): Ground Pin.

IN

LT3502A’s internal regulator and to the internal power

DA (Pin 6): Connect the catch diode (D1) anode to this

pin. This pin is used to provide frequency foldback in

extreme situations.

switch. This pin must be locally bypassed.

BD (Pin 2): The BD pin is used to provide current to the

internal boost Schottky diode.

BOOST (Pin 7): The BOOST pin is used to provide a drive

voltage,higherthantheinputvoltage,totheinternalbipolar

NPN power switch. Connect a boost capacitor from this

pin to SW Pin.

FB (Pin 3): The LT3502/LT3502A regulate their feedback

pin to 0.8V. Connect the feedback resistor divider tap to

this pin. Set the output voltage according to V

+ R1/R2). A good value for R2 is 10k.

= 0.8(1

OUT

SW (Pin 8): The SW pin is the output of the internal power

switch. Connect this pin to the inductor, catch diode and

boost capacitor.

⎯

SHDN (Pin 4): The SHDN pin is used to put the LT3502 in

shutdown mode. Tie to ground to shut down the LT3502/

LT3502A. Tie to 2V or more for normal operation. If the

shutdown feature is not used, tie this pin to the V pin.

The SHDN pin also provides soft-start and frequency

foldback. To use the soft-start feature, connect R3 and

C4 to the SHDN pin. SHDN Pin voltage should not be

higher than V .

IN

⎯

IN

BLOCK DIAGRAM

V

IN

V

1

IN

C2

INT REG

AND

UVLO

BD

2

BOOST

7

Σ

ON OFF

SLOPE

COMP

R

S

Q

R3

SHDN

C3

L1

C1

4

Q

DRIVER

Q1

C4

SW

V

8

OUT

OSC

D1

FREQUENCY

FOLDBACK

DA

6

5

V

C

g

m

GND

0.8V

FB

3

R2

R1

3502 BD

3502f

6

LT3502/LT3502A

OPERATION

The LT3502/LT3502A are constant frequency, current

mode step-down regulators. An oscillator enables an RS

ﬂip-ﬂop, turning on the internal 500mA power switch Q1.

An ampliﬁer and comparator monitor the current ﬂowing

The switch driver operates from either V or from the

IN

BOOST pin. An external capacitor and the internal diode

are used to generate a voltage at the BOOST pin that is

higher than the input supply. This allows the driver to

fully saturate the internal bipolar NPN power switch for

efﬁcient operation.

between the V and SW pins, turning the switch off when

IN

this current reaches a level determined by the voltage at

V .Anerrorampliﬁermeasurestheoutputvoltagethrough

C

A comparator monitors the current ﬂowing through the

catch diode via the DA pin and reduces the LT3502/

LT3502A’s operating frequency when the DA pin current

exceeds the 650mA valley current limit. This frequency

foldback helps to control the output current in fault con-

ditions such as shorted output with high input voltage.

The DA comparator works in conjunction with the switch

peak current limit comparator to determine the maximum

deliverable current of the LT3502/LT3502A. The peak

current limit comparator is used in normal current mode

operations and is used to turn off the switch. The DA val-

ley current comparator monitors the catch diode current

and will delay switching until the catch diode current is

below the 650mA limit. Maximum deliverable current to

the output is therefore limited by both switch peak current

limit and DA valley current limit.

an external resistor divider tied to the FB pin and servos

theV node. Iftheerrorampliﬁer’soutputincreases, more

C

current is delivered to the output; if it decreases, less cur-

rent is delivered. An active clamp (not shown) on the V

C

node provides current limit. The V node is also clamped

C

⎯

to the voltage on the SHDN pin; soft-start is implemented

by generating a voltage ramp at the SHDN pin using an

⎯ ⎯ ⎯ ⎯

external resistor and capacitor. The SHDN pin voltage

during soft-start also reduces the oscillator frequency to

avoid hitting current limit during start-up.

An internal regulator provides power to the control cir-

cuitry. This regulator includes an undervoltage lockout to

⎯

prevent switching when V is less than ~3V. The SHDN

IN

pin is used to place the LT3502/LT3502A in shutdown,

disconnecting the output and reducing the input current

to less than 2μA.

3502f

7

LT3502/LT3502A

APPLICATIONS INFORMATION

FB Resistor Network

transient inputs up to the absolute maximum ratings of

the V and BOOST pins. The input voltage should be

IN

The output voltage is programmed with a resistor divider

between the output and the FB pin. Choose the 1% resis-

tors according to:

limited to the V operating range (40V) during overload

IN

conditions.

Minimum On Time

V

0.8V

⎛

⎞

⎠

OUT

R1= R2

– 1

⎜

⎝

⎟

The LT3502/LT3502A will still regulate the output at input

voltages that exceed V

(up to 40V), however, the

IN(MAX)

R2 should be 20k or less to avoid bias current errors.

Reference designators refer to the Block Diagram.

output voltage ripple increases as the input voltage is

increased.

Input Voltage Range

As the input voltage is increased, the part is required to

switch for shorter periods of time. Delays associated with

turning off the power switch dictate the minimum on time

ofthepart. TheminimumontimefortheLT3502/LT3502A

is 60ns (Figure 1).

The input voltage range for the LT3502/LT3502A applica-

tions depends on the output voltage and on the absolute

maximum ratings of the V and BOOST pins.

IN

The minimum input voltage is determined by either the

LT3502/LT3502A’s minimum operating voltage of 3V, or

by its maximum duty cycle. The duty cycle is the fraction

of time that the internal switch is on and is determined

by the input and output voltages:

When the required on time decreases below the minimum

ontimeof60ns,insteadoftheswitchpulsewidthbecoming

narrower to accommodate the lower duty cycle require-

ment, the switch pulse width remains ﬁxed at 60ns. The

inductorcurrentrampsuptoavalueexceedingtheloadcur-

rentandtheoutputrippleincreases. Thepartthenremains

off until the output voltage dips below the programmed

value before it begins switching again (Figure 2).

V_OUT+ V_D

DC =

V – V_SW+ V_D

IN

where V is the forward voltage drop of the catch diode

D

(~0.4V) and V is the voltage drop of the internal switch

Provided that the load can tolerate the increased output

voltagerippleandthatthecomponentshavebeenproperly

SW

(~0.45Vatmaximumload). Thisleadstoaminimuminput

voltage of:

selected, operation above V

damage the part.

is safe and will not

IN(MAX)

V_OUT+ V_D

DC_MAX

V

=

– V_D+ V_SW

IN(MIN)

As the input voltage increases, the inductor current ramps

up quicker, the number of skipped pulses increases and

with DC

LT3502.

= 0.80 for the LT3502A and 0.90 for the

MAX

V

SW

The maximum input voltage is determined by the absolute

20V/DIV

maximum ratings of the V and BOOST pins. For ﬁxed

IN

frequency operation, the maximum input voltage is de-

I

L

termined by the minimum duty cycle DC

:

500mA/DIV

MIN

V

OUT

100mV/DIV

V_OUT+ V_D

DC_MIN

V

=

– V_D+ V_SW

3502 F01

IN(MAX)

V

= 33V

1μs/DIV

IN

OUT

= 3.3V

L = 6.8μH

C

I

= 10μF

OUT

DC

= 0.10 for the LT3502A and 0.05 for the LT3502.

= 250mA

MIN

OUT

Note that this is a restriction on the operating input volt-

age for ﬁxed frequency operation; the circuit will tolerate

Figure 1. Continuous Mode Operation Near

Minimum On Time of 60ns.

3502f

8

LT3502/LT3502A

APPLICATIONS INFORMATION

V

SW

20V/DIV

I

L

I

500mA/DIV

L

500mA/DIV

V

OUT

100mV/DIV

3502 F03

3502 F02

V

= 40V

1μs/DIV

V

= 40V

1μs/DIV

IN

OUT

IN

OUT

= 3.3V

L = 6.8μH

C

I

= 10μF

= 500mA

C

I

= 10μF

= 250mA

OUT

Figure 3. Pulse Skip with Large Load Current Will be Limited

by the DA Valley Current Limit. Notice the Flat Inductor Valley

Current and Reduced Switching Frequency

Figure 2. Pulse Skip Occurs when

Required On Time is Below 60ns

the output voltage ripple increases. For operation above

IN(MAX)

components be adequately rated for operation at the

intended voltage levels.

Inductor Selection and Maximum Output Current

V

the only component requirement is that the

A good ﬁrst choice for the inductor value is:

L = 1.6(V

L = 4.6(V

+ V ) for the LT3502A

D

OUT

Inductor current may reach current limit when operating

in pulse skip mode with small valued inductors. In this

case, the LT3502/LT3502A will periodically reduce its

frequency to keep the inductor valley current to 650mA

(Figure 3). Peak inductor current is therefore peak current

plus minimum switch delay:

+ V ) for the LT3502

D

where V is the voltage drop of the catch diode (~0.4V)

D

and L is in μH. With this value there will be no subhar-

monicoscillationforapplicationswith50%orgreaterduty

cycle. The inductor’s RMS current rating must be greater

than the maximum load current and its saturation current

should be about 30% higher. For robust operation during

fault conditions, the saturation current should be above

1.2A. To keep efﬁciency high, the series resistance (DCR)

should be less than 0.1Ω. Table 1 lists several vendors

and types that are suitable.

V – V_OUT

IN

900mA +

• 60ns

L

The part is robust enough to survive prolonged operation

under these conditions as long as the peak inductor cur-

rent does not exceed 1.2A. Inductor current saturation

and junction temperature may further limit performance

during this operating regime.

Table 1

VENDOR

URL

PART SERIES

INDUCTANCE RATE (μH)

SIZE (mm)

Sumida

www.sumida.com

CDRH4D28

CDRH5D28

CDRH8D28

1.2 to 4.7

2.5 to 10

2.5 to 33

4.5 × 4.5

5.5 × 5.5

8.3 × 8.3

Toko

www.toko.com

A916CY

D585LC

2 to 12

1.1 to 39

6.3 × 6.2

8.1 × 8

Würth Elektronik

www.we-online.com

WE-TPC(M)

WE-PD2(M)

WE-PD(S)

1 to 10

2.2 to 22

1 to 27

4.8 × 4.8

5.2 × 5.8

7.3 × 7.3

3502f

9

LT3502/LT3502A

APPLICATIONS INFORMATION

There are several graphs in the Typical Performance

Characteristics section of this data sheet that show the

maximum load current as a function of input voltage and

inductor value for several popular output voltages. Low

inductance may result in discontinuous mode opera-

tion, which is okay, but further reduces maximum load

current. For details of the maximum output current and

discontinuous mode operation, see Linear Technology

Application Note 44.

LT3502/LT3502A’s voltage rating. This situation is easily

avoided; see the Hot Plugging Safely section.

Output Capacitor

The output capacitor has two essential functions. Along

with the inductor, it ﬁlters the square wave generated by

theLT3502/LT3502AtoproducetheDCoutput. Inthisrole

it determines the output ripple so low impedance at the

switchingfrequencyisimportant.Thesecondfunctionisto

storeenergyinordertosatisfytransientloadsandstabilize

the LT3502/LT3502A’s control loop. Ceramic capacitors

have very low equivalent series resistance (ESR) and

provide the best ripple performance. A good value is:

Catch Diode

Alowcapacitance500mASchottkydiodeisrecommended

for the catch diode, D1. The diode must have a reverse

voltage rating equal to or greater than the maximum input

voltage. The Phillips PMEG4005AEA is a good choice; it

is related for 500mA continuous forward current and a

maximum reverse voltage of 40V.

33

V_OUT

C_OUT

=

for the LT3502A

for the LT3502

66

V_OUT

C_OUT

=

Input Capacitor

where C

is in μF. Use an X5R or X7R type and keep

OUT

Bypass the input of the LT3502/LT3502A circuit with a 1μF

or higher value ceramic capacitor of X7R or X5R type. Y5V

typeshavepoorperformanceovertemperatureandapplied

voltageandshouldnotbeused. A1μFceramicisadequate

to bypass the LT3502/LT3502A and will easily handle the

ripple current. However, if the input power source has

high impedance, or there is signiﬁcant inductance due to

long wires or cables, additional bulk capacitance may be

necessary. This can be provided with a low performance

electrolytic capacitor.

in mind that a ceramic capacitor biased with V

will

OUT

have less than its nominal capacitance. This choice will

provide low output ripple and good transient response.

Transient performance can be improved with a high value

capacitor, but a phase lead capacitor across the feedback

resistor, R1, may be required to get the full beneﬁt (see

the Compensation section).

For small size, the output capacitor can be chosen

according to:

Step-down regulators draw current from the input supply

in pulses with very fast rise and fall times. The input ca-

pacitor is required to reduce the resulting voltage ripple at

the LT3502/LT3502A and to force this very high frequency

switchingcurrentintoatightlocalloop, minimizingEMI. A

1μF capacitor is capable of this task, but only if it is placed

close to the LT3502/LT3502A and the catch diode (see the

PCB Layout section). A second precaution regarding the

ceramicinputcapacitorconcernsthemaximuminputvolt-

ageratingoftheLT3502/LT3502A.Aceramicinputcapaci-

tor combined with trace or cable inductance forms a high

quality(underdamped)tankcircuit.IftheLT3502/LT3502A

circuit is plugged into a live supply, the input voltage can

ring to twice its nominal value, possibly exceeding the

25

V_OUT

C_OUT

=

where C

is in μF. However, using an output capacitor

thissmallresultsinanincreasedloopcrossoverfrequency

and increased sensitivity to noise.

OUT

High performance electrolytic capacitors can be used for

theoutputcapacitor. LowESRisimportant, sochooseone

that is intended for use in switching regulators. The ESR

should be speciﬁed by the supplier and should be 0.1Ω

or less. Such a capacitor will be larger than a ceramic

capacitor and will have a larger capacitance, because the

capacitor must be large to achieve low ESR. Table 2 lists

several capacitor vendors.

3502f

10

LT3502/LT3502A

APPLICATIONS INFORMATION

Figure4showsthetransientresponseoftheLT3502Awith

several output capacitor choices. The output is 3.3V. The

loadcurrentissteppedfrom150mAto400mAandbackto

150mA, and the oscilloscope traces show the output volt-

age. The upper photo shows the recommended value. The

second photo shows the improved response (less voltage

Table 2

VENDOR

Panasonic

PHONE

(714) 373-7366

URL

PART SERIES

COMMENTS

EEF Series

T494,T495

www.panasonic.com

Ceramic

Polymer,

Tantalum

Ceramic,

Tantalum

Ceramic

Polymer,

Tantalum

Kemet

Sanyo

(864) 963-6300

(408)794-9714

www.kemet.com

www.sanyovideo.com

POSCAP

Murata

AVX

(404) 436-1300

(864) 963-6300

www.murata.com

www.avxcorp.com

Ceramic

Ceramic,

Tantalum

TPS Series

Taiyo Yuden

www.taiyo-yuden.com

Ceramic

10μs/DIV

V

OUT

32.4k

FB

I

L

0.2A/DIV

10μF

V

OUT

10k

0.1V/DIV

AC COUPLED

3502 F04a

3502 F04b

3502 F04c

V

OUT

32.4k

FB

10k

50pF

I

L

10μF

×2

0.2A/DIV

V

OUT

0.1V/DIV

AC COUPLED

V

OUT

32.4k

FB

10k

+

I

L

100μF

0.2A/DIV

V

OUT

SANYO

4TPB100M

0.1V/DIV

AC COUPLED

Figure 4. Transient Load Response of the LT3502A with Different Output Capacitors

as the Load Current is Stepped from 150mA to 400mA. V_IN= 12V, V_OUT= 3.3V, L = 6.8μH

3502f

11

LT3502/LT3502A

APPLICATIONS INFORMATION

drop) resulting from a larger output capacitor and a phase

leadcapacitor.Thelastphotoshowstheresponsetoahigh

performanceelectrolyticcapacitor.Transientperformance

is improved due to the large output capacitance.

start-up, the minimum input voltage is also limited by the

boost circuit. If the input voltage is ramped slowly, or the

⎯

LT3502/LT3502A is turned on with its SHDN pin when the

output is already in regulation, then the boost capacitor

may not be fully charged. Because the boost capacitor is

charged with the energy stored in the inductor, the circuit

will rely on some minimum load current to get the boost

circuit running properly. This minimum load will depend

on the input and output voltages, and on the arrangement

of the boost circuit. The minimum load generally goes to

zero once the circuit has started. Figure 6 shows plots of

minimum load to start and to run as a function of input

voltage. In many cases the discharged output capacitor

will present a load to the switcher which will allow it to

BOOST Pin Considerations

Capacitor C3 and the internal boost diode are used to

generate a boost voltage that is higher than the input

voltage. In most cases a 0.1ꢀF capacitor will work well.

Figure 5 shows two ways to arrange the boost circuit. The

BOOST pin must be at least 2.2V above the SW pin for

best efﬁciency. For outputs of 3V and above, the standard

circuit (Figure 5a) is best. For outputs less than 3V and

above 2.5V, place a discrete Schottky diode (such as the

start. The plots show the worst-case situation where V

IN

BAT54)inparallelwiththeinternaldiodetoreduceV . The

D

is ramping very slowly. At light loads, the inductor current

becomes discontinuous and the effective duty cycle can

be very high. This reduces the minimum input voltage to

following equations can be used to calculate and minimize

boost capacitance in ꢀF:

0.012/(V + V

– V – 2.2) for the LT3502A

D

BD

CATCH

approximately400mVaboveV .Athigherloadcurrents,

OUT

the inductor current is continuous and the duty cycle is

limitedbythemaximumdutycycleoftheLT3502/LT3502A,

requiring a higher input voltage to maintain regulation.

0.030/(V + V

– V – 2.2) for the LT3502

D

BD

V is the forward drop of the boost diode, and V

is

D

CATCH

the forward drop of the catch diode (D1).

Soft-Start

⎯ ⎯ ⎯ ⎯

For lower output voltages the BD pin can be tied to an

external voltage source with adequate local bypassing

(Figure 5b). The above equations still apply for calculating

the optimal boost capacitor for the chosen BD voltage.

The absence of BD voltage during startup will increase

minimum voltage to start and reduce efﬁciency. You must

also be sure that the maximum voltage rating of BOOST

pin is not exceeded.

TheSHDNpincanbeusedtosoftstarttheLT3502/LT3502A,

reducing the maximum input current during start-up. The

⎯

SHDN pin is driven through an external RC ﬁlter to create

a voltage ramp at this pin. Figure 7 shows the start-up

waveforms with and without the soft-start circuit. By

choosing a large RC time constant, the peak start up

current can be reduced to the current that is required to

regulate the output, with no overshoot. Choose the value

The minimum operating voltage of an LT3502/LT3502A

applicationislimitedbytheundervoltagelockout(3V)and

by the maximum duty cycle as outlined above. For proper

⎯

of the resistor so that it can supply 80μA when the SHDN

pin reaches 2V.

V

DD

BD

BOOST

V

LT3502

GND

V

OUT

V

SW

IN

V

IN

LT3502

GND

V

OUT

V

SW

IN

DA

V

– V

BOOST

V

IN

3502 F05a

BOOST

SW

OUT

V

– V ≅ V

BOOST

3502 F05b

BOOST

SW

IN

MAX V

V

+ V

OUT

MAX V

≅ 2V

(5a)

(5b)

Figure 5

3502f

12

LT3502/LT3502A

APPLICATIONS INFORMATION

8

7

6

5

4

3

2

1

7

6

5

START

RUN

START

4

3

RUN

2

1

0

0.001

0.01

0.1

1

0.1

0.01

LOAD CURRENT (A)

1

0.001

LOAD CURRENT (A)

3502 G20

3502 G19

(6a) LT3502A Typical Minimum Input Voltage, V_OUT= 3.3V

(6b) LT3502A Typical Minimum Input Voltage, V_OUT= 5V

7

6

5

8

7

START

6

5

4

3

2

1

RUN

START

RUN

4

3

2

1

0

0.1

LOAD CURRENT (A)

1

0.001

0.01

0.001

0.01

0.1

1

LOAD CURRENT (A)

3502 G22

3502 G21

(6c) LT3502 Typical Minimum Input Voltage, V_OUT= 3.3V

(6d) LT3502 Typical Minimum Input Voltage, V_OUT= 5V

Figure 6

⎯ ⎯ ⎯ ⎯

mA in this state. If you ground the SHDN pin, the SW

pin current will drop to essentially zero. However, if the

Short and Reverse Protection

Iftheinductorischosensothatitwon’tsaturateexcessively,

the LT3502/LT3502A will tolerate a shorted output. When

operating in short-circuit condition, the LT3502/LT3502A

willreducetheirfrequencyuntilthevalleycurrentis650mA

(Figure 8a). There is another situation to consider in sys-

tems where the output will be held high when the input to

the LT3502/LT3502A is absent. This may occur in battery

charging applications or in battery backup systems where

a battery or some other supply is diode OR-ed with the

V

pin is grounded while the output is held high, then

IN

parasitic diodes inside the LT3502/LT3502A can pull large

currents from the output through the SW pin and the V

IN

pin. Figure 8b shows a circuit that will run only when the

inputvoltageispresentandthatprotectsagainstashorted

or reversed input.

Hot Plugging Safely

The small size, robustness and low impedance of ceramic

capacitorsmakethemanattractiveoptionfortheinputby-

passcapacitorofLT3502/LT3502Acircuits.However,these

capacitors can cause problems if the LT3502/LT3502A

LT3502/LT3502A’s output. If the V pin is allowed to ﬂoat

IN

⎯

and the SHDN pin is held high (either by a logic signal

or because it is tied to V ), then the LT3502/LT3502A’s

IN

internal circuitry will pull its quiescent current through

are plugged into a live supply (see Linear Technology

its SW pin. This is ﬁne if your system can tolerate a few

3502f

13

LT3502/LT3502A

APPLICATIONS INFORMATION

V

SW

10V/DIV

RUN

SHDN

GND

I

L

500mA/DIV

3502 F07a

V

OUT

2V/DIV

5μs/DIV

V

= 12V

IN

OUT

= 3.3V

L = 6.8μH

C

= 10μF

OUT

RUN

50k

V

SW

10V/DIV

SHDN

GND

I

0.1μF

L

500mA/DIV

3502 F07b

V

OUT

2V/DIV

3502 F07

50μs/DIV

V

= 12V

IN

= 3.3V

OUT

L = 6.8μH

C

= 10μF

OUT

⎯ ⎯ ⎯ ⎯

Figure 7. To Soft Start the LT3502A, Add a Resistor and Capacitor to the SHDN Pin

D4

BD

V

BOOST

SW

IN

V

SW

10V/DIV

V

OUT

LT3502A

DA

FB

+

I

SHDN

L

500mA/DIV

GND

3502 F08a

3502 F08b

V

= 40V

2μs/DIV

IN

= 0V

OUT

L = 6.8μH

Figure 8b. Diode D4 Prevents a Shorted Input from Discharging

a Backup Battery Tied to the Output; it Also Protects the Circuit

from a Reversed Input. The LT3502/LT3502A Runs Only When

the Input is Present

C

= 10μF

OUT

Figure 8a. The LT3502A Reduces its Frequency to Below 250kHz

to Protect Against Shorted Output with 40V Input

will be plugging the LT3502/LT3502A into an energized

supply, the input network should be designed to prevent

this overshoot. Figure 9 shows the waveforms that result

when an LT3502/LT3502A circuit is connected to a 24V

supply through six feet of 24-gauge twisted pair. The ﬁrst

plot is the response with a 2.2μF ceramic capacitor at the

input. The input voltage rings as high as 35V and the input

3502f

Application Note 88 for a complete discussion). The low

loss ceramic capacitor combined with stray inductance in

series with the power source forms an underdamped tank

circuit,andthevoltageattheV pinoftheLT3502/LT3502A

IN

can ring to twice the nominal input voltage, possibly ex-

ceeding the LT3502/LT3502A’s rating and damaging the

part. If the input supply is poorly controlled or the user

14

LT3502/LT3502A

APPLICATIONS INFORMATION

current peaks at 20A. One method of damping the tank

circuit is to add another capacitor with a series resistor to

the circuit. In Figure 9b an aluminum electrolytic capacitor

has been added. This capacitor’s high equivalent series

resistance damps the circuit and eliminates the voltage

overshoot. The extra capacitor improves low frequency

rippleﬁlteringandcanslightlyimprovetheefﬁciencyofthe

circuit,thoughitislikelytobethelargestcomponentinthe

circuit. An alternative solution is shown in Figure 9c. A 1Ω

resistor is added in series with the input to eliminate the

CLOSING SWITCH

SIMULATES HOT PLUG

I

IN

V

IN

DANGER!

LT3502

2.2μF

V

IN

20V/DIV

RINGING V MAY EXCEED

IN

ABSOLUTE MAXIMUM

RATING OF THE LT3502

+

I

IN

5A/DIV

LOW

STRAY

IMPEDANCE

ENERGIZED

24V SUPPLY

INDUCTANCE

DUE TO 6 FEET

(2 METERS) OF

TWISTED PAIR

20μs/DIV

(9a)

V

LT3502

2.2μF

IN

20V/DIV

+

10μF

35V

AI.EI.

I

IN

5A/DIV

(9b)

20μs/DIV

1Ω

V

LT3502

2.2μF

IN

20V/DIV

0.1μF

I

IN

5A/DIV

3502 F09

20μs/DIV

(9c)

Figure 9. A Well Chosen Input Network Prevents Input Voltage Overshoot and

Ensures Reliable Operation When the LT3502 is Connected to a Live Supply

CURRENT MODE

POWER STAGE

LT3502

–

0.5V

SW

g

=

m

OUT

1A/V

+

C

R1

PL

–

+

FB

g

=

V

C

m

100μA/V

ESR

800mV

R

C

C1

ERROR

AMPLIFIER

+

150k

C1

C

1M

70pF

R2

GND

3502 F10

Figure 10. Model for Loop Response

3502f

15

LT3502/LT3502A

APPLICATIONS INFORMATION

voltage overshoot (it also reduces the peak input current).

A 0.1μF capacitor improves high frequency ﬁltering. This

solution is smaller and less expensive than the electrolytic

capacitor. For high input voltages its impact on efﬁciency

is minor, reducing efﬁciency less than one half percent for

a 5V output at full load operating from 24V.

PCB Layout

ForproperoperationandminimumEMI,caremustbetaken

during printed circuit board layout. Figure 11 shows the

recommended component placement with trace, ground

plane and via locations. Note that large, switched currents

ﬂow in the LT3502/LT3502A’s V and SW pins, the catch

IN

diode(D1)andtheinputcapacitor(C2).Theloopformedby

these components should be as small as possible and tied

to system ground in only one place. These components,

along with the inductor and output capacitor, should be

placed on the same side of the circuit board, and their

connections should be made on that layer. Place a local,

unbroken ground plane below these components, and tie

thisgroundplanetosystemgroundatonelocation, ideally

at the ground terminal of the output capacitor C1. The SW

and BOOST nodes should be as small as possible. Finally,

keep the FB node small so that the ground pin and ground

traceswillshielditfromtheSWandBOOSTnodes.Include

vias near the exposed GND pad of the LT3502/LT3502A

to help remove heat from the LT3502/LT3502A to the

ground plane.

Frequency Compensation

TheLT3502/LT3502Ausecurrentmodecontroltoregulate

theoutput.Thissimpliﬁesloopcompensation.Inparticular,

theLT3502/LT3502AdoesnotrequiretheESRoftheoutput

capacitorforstabilityallowingtheuseofceramiccapacitors

to achieve low output ripple and small circuit size.

Figure 10 shows an equivalent circuit for the LT3502/

LT3502Acontrolloop.Theerrorampisatransconductance

ampliﬁerwithﬁniteoutputimpedance. Thepowersection,

consisting of the modulator, power switch and inductor,

is modeled as a transconductance ampliﬁer generating an

output current proportional to the voltage at the V node.

C

Note that the output capacitor integrates this current, and

that the capacitor on the V node (C ) integrates the er-

C

ror ampliﬁer output current, resulting in two poles in the

loop. R provides a zero. With the recommended output

C

capacitor, the loop crossover occurs above the R C zero.

C C

V

OUT

This simple model works well as long as the value of the

inductor is not too high and the loop crossover frequency

is much lower than the switching frequency. With a larger

ceramiccapacitor(verylowESR),crossovermaybelower

C1

L1

C2

and a phase lead capacitor (C ) across the feedback

PL

V

IN

C3

divider may improve the phase margin and transient

response. Large electrolytic capacitors may have an ESR

large enough to create an additional zero, and the phase

lead may not be necessary.

D1

BST

DA

FB

R1

BD

SHDN

R2

GND

If the output capacitor is different than the recommended

capacitor, stability should be checked across all operating

conditions, including load current, input voltage and tem-

perature.TheLT1375datasheetcontainsamorethorough

discussion of loop compensation and describes how to

test the stability using a transient load.

3502 F11

= VIA

Figure 11

3502f

16

LT3502/LT3502A

APPLICATIONS INFORMATION

High Temperature Considerations

10V

BD

ThedietemperatureoftheLT3502/LT3502Amustbelower

than the maximum rating of 125°C. This is generally not

a concern unless the ambient temperature is above 85°C.

Forhighertemperatures,careshouldbetakeninthelayout

of the circuit to ensure good heat sinking of the LT3502/

LT3502A.Themaximumloadcurrentshouldbederatedas

the ambient temperature approaches 125°C. The die tem-

perature is calculated by multiplying the LT3502/LT3502A

power dissipation by the thermal resistance from junction

toambient. PowerdissipationwithintheLT3502/LT3502A

can be estimated by calculating the total power loss from

anefﬁciencymeasurementandsubtractingthecatchdiode

loss. The resulting temperature rise at full load is nearly

independentofinputvoltage. Thermalresistancedepends

on the layout of the circuit board, but 102°C/W is typical

for the (2mm × 2mm) DFN package.

V

IN

V

BOOST

IN

3.5V TO 40V

L1

C3

0.1μF

C2

1μF

33μH

V

OUT

SW

DA

15V

500mA

LT3502A

22pF

R1

180k

SHDN

FB

OFF ON

R2

10k

C1

10μF

GND

3502 F12

Figure 12. 15V Step-Down Converter

how to overcome this limitation using an additional zener

diode.

Other Linear Technology Publications

Application notes AN19, AN35 and AN44 contain more

detailed descriptions and design information for Buck

regulators and other switching regulators. The LT1376

data sheet has a more extensive discussion of output

ripple, loop compensation and stability testing. Design

Note 100 shows how to generate a bipolar output supply

using a buck regulator.

Outputs Greater Than 7V

Note that for outputs above 7V, the input voltage range

will be limited by the maximum rating of the BOOST pin.

The sum of input and output voltages cannot exceed the

BOOSTpin’s50Vrating. The15Vcircuit(Figure12)shows

TYPICAL APPLICATIONS

0.8V Step-Down Converter

V

BD

3V TO 7V

BD

3V TO 7V

0.1μF

BD

V

IN

V

IN

BOOST

SW

V

BOOST

SW

IN

3V TO 40V

L1

10μH

C3

0.1μF

L1

3.3μH

C2

1μF

C3

C2

1μF

V

OUT

0.8V

0.1μF

OUT

0.8V

500mA

LT3502

D1

LT3502A

D1

DA

FB

DA

FB

SHDN

OFF ON

SHDN

OFF ON

C1

100μF

GND

C1

47μF

GND

C1: JMK316BJ107ML

L1: LQH43CN100K03

C1: JMK212BJ476MG

C3: HMK212BJ104MG

L1: LQH43CN3R3M03

3502TA02b

3502TA02a

3502f

17

LT3502/LT3502A

TYPICAL APPLICATIONS

1.8V Step-Down Converter

V

BD

3V TO 7V

0.1μF

BD

V

IN

V

IN

3V TO 40V

V

BOOST

SW

IN

V

BOOST

SW

IN

3V TO 40V

L1

4.7μH

C2

1μF

C3

L1

15μH

C2

1μF

C3

V

0.1μF

OUT

V

OUT

0.1μF

1.8V

500mA

LT3502A

D1

LT3502

D1

DA

FB

DA

FB

R1

12.5k

SHDN

OFF ON

SHDN

OFF ON

R2

10k

C1

22μF

GND

R2

10k

C1

47μF

GND

C1: JMK212BJ226MG

L1: LQH43CN4R7M03

C1: JMK212BJ476MG

L1: LQH55DN150M03

3502TA03a

3502TA03b

2.5V Step-Down Converter

V

BD

3V TO 7V

0.1μF

BD

V

IN

3.5V TO 40V

IN

V

BOOST

C3

V

BOOST

IN

3.5V TO 40V

L1

6.8μH

L1

15μH

C2

1μF

C2

1μF

C3

0.1μF

V

0.1μF

OUT

2.5V

SW

DA

FB

SW

DA

FB

2.5V

500mA

LT3502A

LT3502

D1

R1

21.3k

R1

21.3k

SHDN

OFF ON

R2

10k

C1

22μF

R2

10k

C1

22μF

GND

C1: JMK212BJ226MG

L1: LQH43DN6R8M03

C1: JMK212BJ226MG

L1: LQH55DN150M03

3502TA04a

3502TA04b

3.3V Step-Down Converter

BD

V

IN

V

BOOST

SW

V

BOOST

IN

4.7V TO 40V

4.5V TO 40V

L1

6.8μH

C3

L1

15μH

C3

0.1μF

C2

1μF

C2

1μF

V

0.1μF

V

OUT

3.3V

SW

DA

FB

500mA

LT3502A

D1

LT3502

D1

DA

FB

R1

31.6k

R1

31.6k

SHDN

OFF ON

SHDN

OFF ON

R2

10k

C1

10μF

GND

R2

10k

C1

22μF

GND

C1: LMK316BJ106ML-BR

L1: LQH43CN6R8M03

C1: JMK212BJ226MG

L1: LQH55DN150M03

3502TA07a

3502TA07b

3502f

18

LT3502/LT3502A

PACKAGE DESCRIPTION

DC Package

8-Lead Plastic DFN (2mm × 2mm)

(Reference LTC DWG # 05-08-1719 Rev Ø)

0.70 0.05

2.55 0.05

0.64 0.05

1.15 0.05

(2 SIDES)

PACKAGE

OUTLINE

0.25 0.05

0.45 BSC

1.37 0.05

(2 SIDES)

RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS

APPLY SOLDER MASK TO AREAS THAT ARE NOT SOLDERED

R = 0.115

TYP

5

8

R = 0.05

TYP

0.40 0.10

PIN 1 NOTCH

2.00 0.10 0.64 0.10

(4 SIDES)

(2 SIDES)

R = 0.20 OR

0.25 × 45°

CHAMFER

PIN 1 BAR

TOP MARK

(SEE NOTE 6)

(DC8) DFN 0106 REVØ

4

1

0.23 0.05

0.45 BSC

0.75 0.05

0.200 REF

1.37 0.10

(2 SIDES)

BOTTOM VIEW—EXPOSED PAD

0.00 – 0.05

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

3502f

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.

19

LT3502/LT3502A

TYPICAL APPLICATION

5V Step-Down Converter

BD

V

IN

V

BOOST

SW

V

BOOST

SW

IN

6.7V TO 40V

6.4V TO 40V

L1

10μH

C3

L1

22μH

C3

C2

1μF

C2

1μF

V

0.1μF

V

0.1μF

OUT

5V

500mA

LT3502A

LT3502

D1

DA

FB

DA

FB

R1

52.3k

SHDN

OFF ON

SHDN

OFF ON

R2

10k

C1

10μF

GND

R2

10k

C1

22μF

GND

C1: LMK316BJ106ML-BR

L1: LQH43CN100K03

C1: LMK316BJ106ML-BR

L1: LQH43CN100K03

3502TA05a

3502TA05b

RELATED PARTS

PART NUMBER

DESCRIPTION

COMMENTS

V : 5.5V to 60V, V

LT1766

60V, 1.2A (I ), 200kHz, High Efﬁciency Step-Down

DC/DC Converter

= 1.2V, I = 2.5mA, I = 25μA,

OUT(MIN) Q SD

OUT

IN

TSSOP16/TSSOP16E Packages

LT1933

500mA (I ), 500kHz, Step-Down Switching Regulator in V : 3.6V to 36V, V

= 1.2V, I = 1.6mA, I < 1μA,

OUT(MIN) Q SD

OUT

IN

SOT-23

ThinSOT^TMPackage

LT1936

36V, 1.4A (I ), 500kHz, High Efﬁciency Step-Down

V : 3.6V to 36V, V

= 1.2V, I = 1.9mA, I < 1μA,

Q SD

OUT

IN

OUT(MIN)

DC/DC Converter

MS8E Package

LT1940

Dual 25V, 1.4A (I ), 1.1MHz, High Efﬁciency Step-Down V : 3.6V to 25V, V

= 1.20V, I = 3.8mA, I < 30μA,

Q SD

OUT

IN

OUT(MIN)

DC/DC Converter

TSSOP16E Package

LT1976/LT1977

60V, 1.2A (I ), 200kHz/500kHz High Efﬁciency Step-

V : 3.3V to 60V, V

= 1.20V, I = 100μA, I < 1μA,

OUT(MIN) Q SD

OUT

IN

Down DC/DC Converters with Burst Mode^®Operation

TSSOP16E Package

LTC 3407/LTC3407-2 Dual 600mA/800mA, 1.5MHz/2.25MHz, Synchronous

Step-DownDC/DC Converters

V : 2.5V to 5.5V, V

= 0.6V, I = 40μA, I <1μA,

Q SD

IN

OUT(MIN)

3mm × 3mm DFN, MS10E Package

LT3434/LT3435

60V, 1.2A (I ), 200kHz/500kHz High Efﬁciency Step-

V : 3.3V to 60V, V = 1.20V, I = 100μA, I < 1μA,

OUT

IN

OUT(MIN)

Q

SD

Down DC/DC Converters with Burst Mode Operation

TSSOP16E Package

LT3437

60V, 400mA (I ), Micropower Step-Down DC/DC

V : 3.3V to 60V, V

= 1.25V, I = 100μA, I < 1μA,

Q SD

OUT

IN

OUT(MIN)

Converter with Burst Mode Operation

DFN Package

LT3493

36V, 1.4A (I ), 750kHz, High Efﬁciency Step-Down

V : 3.6V to 36V, V

= 0.8V, I = 1.9mA, I < 1μA,

Q SD

OUT

IN

DC/DC Converter

DFN Package

LT3501

Dual 25V, 3A (I ), 1.5MHz, High Efﬁciency Step-Down

V : 3.3V to 25V, V

= 0.8V, I = 3.7mA, I < 10μA,

Q SD

OUT

IN

DC/DC Converter

TSSOP20E Package

LT3503

20V, 1A (I ), 2.2MHz, High Efﬁciency Step-Down

V : 3.6V to 20V, V

= 0.78V, I = 1.9mA, I < 1μA,

OUT(MIN) Q SD

OUT

IN

DC/DC Converter

2mm × 3mm DFN Package

V : 3.6V to 36V, V = 0.78V, I = 2mA, I < 2μA,

OUT(MIN) Q SD

LT3505

36V, 1.2A (I ), 3MHz, High Efﬁciency Step-Down

OUT

IN

DC/DC Converter

3mm × 3mm DFN, MS8E Packages

LT3506/LT3506A

LT3508

Dual 25V, 1.6A (I ), 575kHz/1.1MHz, High Efﬁciency

V : 3.6V to 25V, V = 0.8V, I = 3.8mA, I < 30μA,

OUT

IN

OUT(MIN)

Q

SD

Step-Down DC/DC Converters

4mm × 5mm DFN Package

Dual 36V, 1.4A (I ), 2.5MHz, High Efﬁciency Step-Down V : 3.6V to 36V, V

= 0.8V, I = 4.3mA, I < 1μA,

Q SD

OUT

IN

OUT(MIN)

DC/DC Converter

4mm × 4mm QFN, TSSOP16E Packages

LT3510

Dual 25V, 2A (I ), 1.5MHz, High Efﬁciency Step-Down

V : 3.3V to 25V, V = 0.8V, I = 3.7mA, I < 10μA,

OUT

IN

OUT(MIN)

Q

SD

DC/DC Converter

TSSOP20E Package

LTC3548

Dual 400mA + 800mA, 2.25MHz Synchronous Step-Down

DC/DC Converter

V : 2.5V to 5.5V, V

= 0.6V, I = 40μA, I < 1μA,

OUT(MIN) Q SD

IN

3mm × 3mm DFN, MS10E Packages

Burst Mode is a registered trademark of Linear Technology Corporation. ThinSOT is a trademark of Linear Technology Corporation.

3502f

LT 0407 • PRINTED IN USA

20 ^{LinearTechnology Corporation}

1630 McCarthy Blvd., Milpitas, CA 95035-7417

●

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


型号：	LT3502EDC
厂家：	Linear
描述：	IC 1.1 A SWITCHING REGULATOR, 1400 kHz SWITCHING FREQ-MAX, PDSO10, 2 X 2 MM, PLASTIC, DFN-10, Switching Regulator or Controller 开关光电二极管
文件：	总20页 (文件大小：457K)
中文：	中文翻译
下载：	下载PDF数据表文档文件

LT3502EDC [Linear]

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