LT3508

Dual Monolithic 1.4A Step-Down

Switching Regulator

FEATURES

n

DESCRIPTION

The

LT

®

3508

is a dual current mode PWM step-down

DC/DC converter with internal power switches capable

of generating two 1.4A outputs. The wide input voltage

range of 3.7V to 36V makes the LT3508 suitable for reg-

ulating power from a wide variety of sources, including

automotive batteries, 24V industrial supplies and unreg-

ulated wall adapters. Both converters are synchronized

to a single oscillator programmable up to 2.5MHz and

run with opposite phases, reducing input ripple current.

Its high operating frequency allows the use of small, low

cost inductors and ceramic capacitors, resulting in low,

predictable output ripple. Each regulator has independent

tracking and soft-start circuits and generates a power

good signal when its output is in regulation, easing power

supply sequencing and interfacing with microcontrollers

and DSPs.

Cycle-by-cycle current limit, frequency foldback and ther-

mal shutdown provide protection against shorted out-

puts, and soft-start eliminates input current surge during

start-up. The low current (<2μA) shutdown mode enables

easy power management in battery-powered systems.

All registered trademarks and trademarks are the property of their respective owners.

n

Wide Input Voltage Range: 3.7V to 36V

Two 1.4A Output Switching Regulators with Internal

Power Switches

Adjustable 250kHz to 2.5MHz Switching Frequency

Synchronizable over the Full Frequency Range

Anti-Phase Switching Reduces Ripple

Uses Small Inductors and Ceramic Capacitors

Accurate Programmable Undervoltage Lockout

Independent Tracking, Soft-Start and Power Good

Circuits Ease Supply Sequencing

Output Adjustable Down to 800mV

Small 4mm × 4mm 24-Pin QFN or 16-Pin Thermally

Enhanced TSSOP Surface Mount Packages

AEC-Q100 Qualified for Automotive Applications

APPLICATIONS

n

Automotive

DSP Power Supplies

Wall Transformer Regulation

DSL and Cable Modems

PCI Express

TYPICAL APPLICATION

3.3V and 5V Dual Output Step-Down Converter with Output Sequencing

V

IN

5.6V TO 36V

ON OFF

4.7µF

V

IN1

V

IN2

BOOST1

OUT1

3.3V

1.4A

6.8µH

0.22µF

SW1

LT3508

35.7k

FB1

V

C1

11.5k

22µF

51k

150pF

1nF

TRACK/SS1

TRACK/SS2

GND

FB2

V

C2

PG1

PG2

43k

10.7k

100k

100pF

POWER

GOOD

10µF

56.2k

SW2

SHDN

BOOST2

0.22µF

10µH

OUT2

5V

1.4A

EFFICIENCY (%)

Efficiency

95

90

85

80

75

70

65

V

IN

= 12V

V

OUT2

= 5V

V

OUT1

= 3.3V

RT/SYNC

52.3k

0

0.5

1

LOAD CURRENT (A)

1.5

3508 TA01b

f

SW

= 700kHz

3508 TA01a

Document Feedback

For more information

www.analog.com

1

Rev. E

LT3508

ABSOLUTE MAXIMUM RATINGS

(Notes 1, 7)

V

IN

Pin Voltage............................................(–0.3V), 40V

BOOST Pin Voltage ...................................................60V

BOOST Above SW Voltage ........................................30V

SHDN,

PG Voltage ....................................................40V

TRACK/SS, FB, RT/SYNC, V

C

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

Operating Junction Temperature Range (Note 2)

LT3508E ............................................ –40°C to 125°C

LT3508I ............................................. –40°C to 125°C

LT3508H ............................................ –40°C to 150°C

Storage Temperature Range

QFN.................................................... –65°C to 150°C

TSSOP ............................................... –65°C to 150°C

Lead Temperature (Soldering, 10 sec)

TSSOP .............................................................. 300°C

PIN CONFIGURATION

TOP VIEW

RT/SYNC

PG1

PG2

TOP VIEW

TRACK/SS1

BOOST1

SW1

V

IN1

V

IN2

SW2

BOOST2

TRACK/SS2

1

2

3

4

5

6

7

8

17

GND

16 FB1

15 V

C1

14 PG1

13 RT/SYNC

12

SHDN

11 PG2

10 V

C2

9

FB2

FB1 1

TRACK/SS1 2

GND 3

GND 4

GND 5

GND 6

7

BOOST1

8

SW1

9 10 11 12

V

IN1

V

IN2

SW2

BOOST2

25

GND

SHDN

V

C1

V

C2

18 FB2

17 TRACK/SS2

16 GND

15 GND

14 GND

13 GND

24 23 22 21 20 19

FE PACKAGE

16-LEAD PLASTIC TSSOP

θ

JA

= 40°C/W,

θ

JC

= 10°C/W

EXPOSED PAD (PIN 17) IS GND AND MUST BE SOLDERED TO PCB

UF PACKAGE

24-LEAD (4mm

×

4mm) PLASTIC QFN

θ

JA

= 40°C/W,

θ

JC

= 10°C/W

EXPOSED PAD (PIN 25) IS GND AND MUST BE SOLDERED TO PCB

ORDER INFORMATION

LEAD FREE FINISH

LT3508EFE#PBF

LT3508IFE#PBF

LT3508HFE#PBF

LT3508EUF#PBF

LT3508IUF#PBF

LT3508HUF#PBF

AUTOMOTIVE PRODUCTS**

LT3508IFE#WPBF

LT3508HFE#WPBF

LT3508IFE#WTRPBF

LT3508HFE#WTRPBF

3508FE

3508HFE

16-Lead Plastic TSSOP

–40°C to 125°C

–40°C to 150°C

TAPE AND REEL

LT3508EFE#TRPBF

LT3508IFE#TRPBF

LT3508HFE#TRPBF

LT3508EUF#TRPBF

LT3508IUF#TRPBF

LT3508HUF#TRPBF

PART MARKING*

3508FE

3508HFE

3508

3508H

PACKAGE DESCRIPTION

16-Lead Plastic TSSOP

24-Lead (4mm × 4mm) Plastic QFN

TEMPERATURE RANGE

–40°C to 125°C

–40°C to 150°C

–40°C to 125°C

–40°C to 150°C

Contact the factory for parts specified with wider operating temperature ranges. *The temperature grade is identified by a label on the shipping container.

Tape and reel specifications.

Some packages are available in 500 unit reels through designated sales channels with #TRMPBF suffix.

**Versions

of this part are available with controlled manufacturing to support the quality and reliability requirements of automotive applications. These

models are designated with a #W suffix. Only the automotive grade products shown are available for use in automotive applications. Contact your

local Analog Devices account representative for specific product ordering information and to obtain the specific Automotive Reliability reports for

these models.

2

Rev. E

For more information

www.analog.com

LT3508

ELECTRICAL CHARACTERISTICS

PARAMETER

Minimum Operating Voltage, V

IN1

Minimum Operating Voltage, V

IN2

V

IN1

Quiescent Current

V

IN2

Quiescent Current

Shutdown Current (V

IN1

+ V

IN2

)

FB Voltage

l

The

l

denotes the specifications which apply over the full operating

temperature range, otherwise specifications are at T

A

= 25°C. V

IN

= 12V unless otherwise noted. (Note 2)

CONDITIONS

l

MIN

l

TYP

3.4

2.5

4.3

320

0.1

MAX

3.7

3.0

5.2

500

2

0.814

0.816

300

UNITS

V

mA

µA

V

nA

%/V

µS

V/V

A/V

V

IN1

= 12V

Not Switching

V

SHDN

= 0.3V

0.790

0.784

0.800

50

0.01

300

600

2.5

FB Pin Bias Current (Note 3)

FB Voltage Line Regulation

Error Amp Transconductance

Error Amp Voltage Gain

V

C

to Switch Current Gain

Switching Frequency

Switching Phase

Maximum Duty Cycle (Note 4)

V

FB

= 0.800V, V

C

= 0.5V

5V < V

IN

< 40V

l

R

T

= 33.2k

R

T

= 33.2k

R

T

= 33.2k

R

T

= 7.50k

R

T

= 169k

R

T

= 33.2k, V

FB

= 0V

Duty Cycle = 15%

I

SW

= 1.5A

l

0.92

150

84

1

180

90

80

98

120

2.6

300

0.01

1.7

1.06

210

MHz

Deg

%

kHz

l

Foldback Frequency

Switch Current Limit (Note 5)

Switch V

CESAT

Switch Leakage Current

Minimum Boost Voltage

Boost Pin Current

TRACK/SS Pin Current

PG Threshold Offset

PG Voltage Output Low

PG Pin Leakage

SHDN

Threshold Voltage

SHDN

Input Current (Note 6)

SHDN

Threshold Current Hysteresis

SYNC Threshold Voltage

SYNC Input Frequency

l

2.0

3.2

1

2.5

50

2.2

110

0.4

1

2.73

10

9.5

1.5

2.5

A

mV

µA

V

mA

µA

mV

V

µA

V

µA

V

MHz

I

SW

= 1.5A, V

BOOST

= 17V

V

TRACK/SS

= 0V

V

FB

Rising

V

FB

= 0.6V, I

PG

= 250µA

V

PG

= 2V

2.53

V

SHDN

= 60mV Above Threshold Voltage

6

5.5

1

0.25

0.8

56

35

1.2

75

0.13

0.01

2.63

8

7.5

1.25

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 2:

The LT3508E is guaranteed to meet performance specifications

from 0°C to 125°C junction temperature. Specifications over the –40°C

to 125°C operating junction temperature range are assured by design,

characterization and correlation with statistical process controls. The

LT3508I is guaranteed over the full –40°C to 125°C operating junction

temperature range. The LT3508H is guaranteed over the full –40°C to

150°C operating junction temperature range. High junction temperatures

degrade operating lifetimes. Operating lifetime is derated at junction

temperatures greater than 125°C.

Note 3:

Current flows out of pin.

Note 4:

V

BOOST

=12V. Circuitry increases the maximum duty cycle of the

LT3508 when V

BOOST

> V

IN

+ 2.5V. See Minimum Operating Voltage in the

Applications Information section for details.

Note 5:

Current limit is guaranteed by design and/or correlation to static

test. Slope compensation reduces current limit at higher duty cycles.

Note 6:

Current flows into pin.

Note 7:

This IC includes overtemperature protection that is intended

to protect the device during momentary overload conditions. Junction

temperature will exceed the maximum operating junction temperature

range when overtemperature protection is active. Continuous operation

above the specified maximum operating junction temperature may impair

device reliability.

For more information

www.analog.com

3

Rev. E

LT3508

TYPICAL PERFORMANCE CHARACTERISTICS

Efficiency, V

OUT

= 5V

95

90

EFFICIENCY (%)

85

80

75

70

65

T

A

= 25°C

f = 700kHz

V

IN

= 12V

V

IN

= 24V

EFFICIENCY (%)

V

IN

= 32V

90

85

80

75

70

65

60

Efficiency, V

OUT

= 3.3V

T

A

= 25°C

f = 700kHz

85

V

IN

= 12V

V

IN

= 24V

80

EFFICIENCY (%)

75

70

65

60

55

Efficiency, V

OUT

= 1.8V

T

A

= 25°C

f = 1MHz

V

IN

= 3.3V

V

IN

= 5V

V

IN

= 12V

V

IN

= 32V

0

0.5

1

LOAD CURRENT (A)

1.5

3508 G01

0

0.5

1

LOAD CURRENT (A)

1.5

3508 G02

0

0.5

1

LOAD CURRENT (A)

1.5

3508 G03

Feedback Voltage

0.810

3.0

2.5

FEEDBACK VOLTAGE (V)

0.805

CURRENT LIMIT (A)

2.0

1.5

1.0

0.5

0.790

–50 –25

Switch Current Limit

vs Temperature

3.0

2.5

CURRENT LIMIT (A)

2.0

1.5

1.0

0.5

0

Switch Current Limit

vs Duty Cycle

T

A

= 25°C

TYPICAL

MINIMUM

0.800

0.795

0

25 50 75 100 125 150

TEMPERATURE (°C)

3508 G04

0

–50 –25

0

25 50 75 100 125 150

TEMPERATURE (°C)

3508 G05

0

20

40

60

DUTY CYCLE (%)

80

100

3508 G06

Switching Frequency vs R

T

175

150

125

R

T

(k )

100

75

50

25

0

0.5

1.0

1.5

FREQUENCY (MHz)

2.0

2.5

3508 G07

Switching Frequency

vs Temperature

1.2

SWITCHING FREQUENCY (MHz)

1.0

0.8

0.6

0.4

0.2

0

–50 –25

R

T

= 33.2k

SWITCHING FREQUENCY (MHz)

3.0

2.5

Switching Frequency Foldback

T

A

= 25°C

R

T

= 7.50k

2.0

1.5

1.0

0.5

0

R

T

= 33.2k

R

T

= 169k

0

100 200 300 400 500 600 700 800

FEEDBACK VOLTAGE (mV)

3508 G09

T

A

= 25°C

0

25 50 75 100 125 150

TEMPERATURE (°C)

3508 G08

4

Rev. E

For more information

www.analog.com

LT3508

TYPICAL PERFORMANCE CHARACTERISTICS

Quiescent Current

5.0

4.5

4.0

INPUT CURRENT (mA)

3.5

3.0

2.5

2.0

1.5

1.0

0.5

0

5

10

V

IN2

15 20 25 30

INPUT VOLTAGE (V)

35

40

0

–50 –25

0

25 50 75 100 125 150

TEMPERATURE (°C)

3508 G11

V

C

Voltages

2.5

35

30

OUTPUT CURRENT (µA)

CLAMP VOLTAGE

25

20

15

10

5

Error Amp Output Current

T

A

= 25°C

V

IN1

2.0

V

C

VOLTAGE (V)

SINKING

1.5

1.0

TO SWITCH

SOURCING

0.5

0

–50 –25

0

25

50

75

100 125 150

3508 G12

TEMPERATURE (°C)

3508 G10

Switch Voltage Drop

350

300

BOOST PIN CURRENT (mA)

SWITCH VOLTAGE (mV)

250

200

150

100

50

0

1

0.5

SWITCH CURRENT (A)

1.5

3508 G13

Boost Pin Current

35

30

25

20

15

10

5

0

1

0.5

SWITCH CURRENT (A)

1.5

3508 G14

T

A

= 25°C

T

A

= 25°C

SHDN Pin Current

120

100

SHDN

PIN CURRENT (µA)

80

60

40

20

0

T

A

= –45°C

T

A

= 125°C

T

A

= 25°C

4.0

3.5

3.0

INPUT VOLTAGE (V)

2.5

2.0

1.5

1.0

0.5

0

5

10 15 20 25 30

SHDN

PIN VOLTAGE (V)

35

40

Undervoltage Lockout

V

IN1

V

IN2

0

–50 –25

0

25 50 75 100 125 150

TEMPERATURE (°C)

3508 G16

3508 G15

For more information

www.analog.com

5

Rev. E

参数名称	属性值
欧盟限制某些有害物质的使用	Compliant
ECCN (US)	EAR99
Part Status	Active
HTS	8542.39.00.01
类型 Type	Synchronous Step Down
输出类型 Output Type	Adjustable
Switching Frequency (kHz)	2500
Switching Regulator	Yes
Number of Outputs	2
Output Voltage (V)	0.8 to 35.28
Maximum Output Current (A)	1.4\|1.4\|1.4\|1.4\|1.4\|1.4\|1.4\|1.4\|1.4\|1.4\|1.4\|1.4\|1.4\|1.4\|1.4\|1.4\|1.4\|1.4\|1.4\|1.4\|1.4\|1.4\|1.4\|1.4\|1.4\|1.4\|1.4\|1.4\|1.4\|1.4\|1.4\|1.4\|1.4\|1.4\|1.4\|1.4\|1.4\|1.4
Minimum Input Voltage (V)	3.7
Maximum Input Voltage (V)	36
Operating Supply Voltage (V)	3.7 to 36
Typical Quiescent Current (uA)	4300
Line Regulation	0.01%/V(Typ)
Minimum Operating Temperature (°C)	-40
Maximum Operating Temperature (°C)	150
Supplier Temperature Grade	Extended
系列 Packaging	Tape and Reel
Pin Count	16
Standard Package Name	SOP
Supplier Package	TSSOP EP
Mounting	Surface Mount
Package Height	0.95(Max)
Package Length	5.1(Max)
Package Width	4.5(Max)
PCB changed	16
Lead Shape	Gull-wing

LT3508HFE#TRPBF

LT3508HFE#TRPBF概述

LT3508HFE#TRPBF规格参数

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