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LT3509

Dual 36V, 700mA

Step-Down Regulator

FEATURES

n

DESCRIPTION

The LT

®

3509 is a dual, current mode, step-down switching

regulator, with internal power switches each capable of

providing 700mA output current. This regulator provides a

compact and robust solution for multi-rail systems in harsh

environments. It incorporates several protection features

including overvoltage lockout and cycle-by-cycle current

limit. Thermal shutdown provides additional protection.

The loop compensation components and the boost diodes

are integrated on-chip. Switching frequency is set by a

single external resistor. External synchronization is also

possible. The high maximum switching frequency allows

the use of small inductors and ceramic capacitors for low

ripple. Constant frequency operation above the AM band

avoids interference with radio reception, making the LT3509

well suited for automotive applications. Each regulator

has an independent shutdown and soft-start control pin.

When both converters are powered down, the common

circuitry enters a low current shutdown state.

L,

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

of Linear Technology Corporation. All other trademarks are the property of their respective

owners.

Two 700mA Switching Regulators with Internal

Power Switches

Wide 3.6V to 36V Operating Range

Overvoltage Lockout Protects Circuit Through 60V

Supply Transients

Short-Circuit Robust

Low Dropout Voltage: 95% Maximum Duty Cycle

Adjustable 300kHz to 2.2MHz Switching Frequency

Synchronizable Over the Full Range

Uses Small Inductors and Ceramic Capacitors

Integrated Boost Diodes

Internal Compensation

Thermally Enhanced 14-Lead (4mm

×

3mm)

DFN and 16 Lead MSOP Packages

APPLICATIONS

n

Automotive Electronics

Industrial Controls

Wall Transformer Regulation

Networking Devices

CPU, DSP, or FPGA Power

TYPICAL APPLICATION

3.3V and 5V Dual Output Step-Down Converter

6.5V TO 36V

(TRANSIENT TO 60V)

2.2μF

V

IN

BOOST1

3.3V

700mA

6.8μH

0.1μF

SW1

LT3509

31.6k

MBRM140

10μF

10.2k

1nF

DA1

FB1

DA2

FB2

MBRM140

53.6k

22μF

SW2

BD

BOOST2

0.1μF 10μH

EFFICIENCY (%)

5V

700mA

90

85

80

V

OUT

= 3.3V

75

70

65

60

1nF

60.4k

f

SW

= 700kHz

10.2k

3509 TA01a

Efﬁciency

V

OUT

= 5V

RUN/SS1 RUN/SS2

SYNC

GND

RT

55

50

0.0

V

IN

= 12V

f

SW

= 700kHz

0.1

0.2

0.3 0.4 0.5

LOAD CURRENT (A)

0.6

0.7

3509 TA01b

3509fc

1

LT3509

ABSOLUTE MAXIMUM RATINGS

(Note 1)

V

IN

Pin (Note 2) ........................................................60V

BD Pin .......................................................................20V

BOOST Pins ..............................................................60V

BOOST Pins above SW .............................................30V

RUN/SS, FB, RT, SYNC pins........................................6V

Operating Junction Temperature Range (Notes 3, 6)

LT3509E ............................................ –40°C to 125°C

LT3509I ............................................. –40°C to 125°C

LT3509H ............................................ –40°C to 150°C

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

Lead Temperature (Soldering, 10 sec.)

MSOP Package ................................................. 300°C

PIN CONFIGURATION

TOP VIEW

DA1

BOOST1

SW1

V

IN

SW2

BOOST2

DA2

1

2

3

4

5

6

7

15

14 FB1

13 RUN/SS1

12 BD

11 SYNC

10 RT

9 RUN/SS2

8 FB2

DA1

BOOST1

SW1

V

IN

V

IN

SW2

BOOST2

DA2

1

2

3

4

5

6

7

8

TOP VIEW

16

15

14

13

12

11

10

9

FB1

RUN/SS1

AGND

BD

SYNC

RT

RUN/SS2

FB2

17

DE14 PACKAGE

14-LEAD (4mm

×

3mm) PLASTIC DFN

θ

JA

= 43°C/W,

θ

JC

= 4.3°C/W

EXPOSED PAD (PIN 15) IS GND, MUST BE SOLDERED TO PCB

MSE PACKAGE

16-LEAD PLASTIC MSOP

θ

JA

= 43°C/W,

θ

JC

= 4.3°C/W

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

ORDER INFORMATION

LEAD FREE FINISH

LT3509EDE#PBF

LT3509IDE#PBF

LT3509EMSE#PBF

LT3509IMSE#PBF

LT3509HMSE#PBF

TAPE AND REEL

LT3509EDE#TRPBF

LT3509IDE#TRPBF

LT3509EMSE#TRPBF

LT3509IMSE#TRPBF

LT3509HMSE#TRPBF

PART MARKING*

3509

PACKAGE DESCRIPTION

14-Lead (4mm

×

3mm) Plastic DFN

14-Lead (4mm

×

3mm) Plastic DFN

16-Lead Plastic MSOP with Exposed Pad

TEMPERATURE RANGE

–40°C to 125°C

–40°C to 150°C

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

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/

3509fc

2

LT3509

ELECTRICAL CHARACTERISTICS

PARAMETER

V

IN

Undervoltage Lockout

V

IN

Overvoltage Lockout

Input Quiescent Current

Input Shutdown Current

Feedback Pin Voltage

Reference Voltage Line Regulation

RUN/SS Shutdown Threshold

RUN/SS Voltage for Full I

OUT

RUN/SS Pin Pull-up Current

Feedback Pin Bias Current (Note 4)

Switch Current Limit

DA Comparator Current Threshold

Boost Pin Current

Switch Leakage Current

Switch Saturation Voltage

Minumum Boost Voltage above Switch

Boost Diode Forward Voltage

Boost Diode Leakage

Switching Frequency

I

SW

= 0.9A (Note 5)

I

SW

= 0.9A

I

BD

= 20mA

V

R

= 30V

R

T

= 40.2kΩ

R

T

= 180kΩ

R

T

= 14.1kΩ

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. (Note 3)

CONDITIONS

MIN

37

Not Switching V

FB

> 0.8V

V(RUN/SS[1,2]) < 0.3V

l

TYP

3.3

38.5

1.9

9

MAX

3.6

40

2.2

15

0.816

0.8

2

1.3

500

1.9

1.2

36

1.0

2.2

0.9

5

1.08

290

2.5

150

UNITS

V

mA

μA

V

%/V

V

μA

nA

A

mA

μA

V

μA

MHz

kHz

MHz

V

ns

0.784

0.4

0.7

0.8

0.01

0.6

1

90

1.4

0.95

22

0.01

0.32

1.5

0.7

0.1

3.6V < V

IN

< 36V

V

FB

= 0.8V

l

1.05

0.7

I

SW

= 0.9A

0.92

237

2.0

1.0

260

2.15

1.0

80

Sync Pin Input Threshold

Switch Minimum Off-Time

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.

Absolute Maximum Voltage at the V

IN

pin is 60V for non-repetitive

1 second transients and 36V for continuous operation.

Note 3.

The LT3509E 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 LT3509I is guaranteed

over the full –40°C to 125°C temperature range. The LT3509H is guaranteed

l

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 4.

Current ﬂows out of pin.

Note 5.

Switch Saturation Voltage is guaranteed by design.

Note 6.

This IC includes overtemperature protection that is intended to protect

the device during momentary overload conditions. Junction temperature will

exceed the maximum operating temperature when overtemperature protection

is active. Continuous operation above the speciﬁed maximum operating

junction temperature may impair device reliability.

3509fc

3

LT3509

TYPICAL PERFORMANCE CHARACTERISTICS

Efﬁciency vs Load Current

V

OUT

= 5V, f

SW

= 2.0MHz

95

90

V

IN

= 12V

85

EFFICIENCY (%)

80

V

IN

= 24V

75

70

65

60

T

A

= 25ºC

95

90

85

80

75

70

65

60

55

0

0.2

0.4

I

LOAD

(A)

3509 G01

Efﬁciency vs Load Current

V

OUT

= 3.3V, f

SW

= 2.0MHz

T

A

= 25ºC

90

85

V

IN

= 12V

80

EFFICIENCY (%)

75

70

65

60

55

0

0.2

0.4

I

LOAD

(A)

3509 G02

Efﬁciency vs Load Current

V

OUT

= 1.8V, f

SW

= 0.7MHz

T

A

= 25ºC

V

IN

= 12V

0.6

0.8

0.6

0.8

50

0

0.2

0.4

I

LOAD

(A)

0.6

0.8

3509 G03

Switch V

CE(SAT)

vs I

SW

0.35

0.3

20

0.25

I

BOOST

(mA)

V

CE(SAT)

(V)

0.2

0.15

0.1

5

0.05

0

15

T

A

= 25ºC

25

I

BOOST

vs I

SW

T

A

= 25ºC

10

0

0.2

0.4

0.6

I

SW

(A)

0.8

1.0

3509 G04

0

0.2

0.4

0.6

I

SW

(A)

0.8

1

3509 G05

Boost Diode Characteristics

1.2

1

FREQUENCY (MHz)

0.8

V

f

(V)

0.6

0.4

0.2

0

1.5

T

A

= 25ºC

2.2

2.0

Frequency vs R

T

A

= 25ºC

1.0

0.5

0

100

BOOST DIODE CURRENT

(mA)

50

150

3509 G06

0

20

40

60

80 100 120 140 160 180

R

T

(kΩ)

3509 G07

3509fc

4

LT3509

TYPICAL PERFORMANCE CHARACTERISTICS

FB Pin Voltage vs Temperature

0.810

1.04

1.03

FEEDBACK PIN VOLTAGE (V)

0.805

NORMALIZED (f

SW

)

MAXIMUM V

IN

(V)

1.02

1.01

1.00

0.99

0.98

0.790

–50 –25

0.97

–50 –25

20

15

10

5

0

f

SW

vs Temperature

(Measured at 1MHz)

30

25

Max V

IN

for Constant Frequency

V

OUT

= 3.3V, f

SW

= 2MHz

T

A

= 25ºC

T

A

= 85ºC

0.800

0.795

0

25 50 75 100 125 150

TEMPERATURE (°C)

3509 G08

0

25 50 75 100 125 150

TEMPERATURE (˚C)

3509 G09

0

0.2

0.4

I

LOAD

(A)

0.6

0.8

3509 G10

Max V

IN

for Constant Frequency

V

OUT

= 5V, f

SW

= 2MHz

45

40

35

MAXIMUM V

IN

(V)

30

25

20

15

10

5

0

0.2

0.4

I

LOAD

(A)

3509 G11

Minimum On-Time vs

Temperature, I

LOAD

= 0.3A

160

140

MINIMUM ON-TIME (ns)

120

100

80

60

40

20

T

A

= 25ºC

T

A

= 85ºC

0.6

0.8

0

–50 –25

0

25 50 75 100 125 150

TEMPERATURE (°C)

3509 G12

I

LIM

vs Temperature

1.5

1.8

1.6

1.3

SWITCH

1.4

1.2

I

LIM

(A)

I

LIM

(A)

1.0

DA

1

0.8

0.6

0.7

0.4

0.2

0.5

–50 –25

0

25 50

75 100 125 150

TEMPERATURE (°C)

3509 G13

I

LIM

vs Duty Cycle

T

A

= 25ºC

0.9

0

10 20 30 40 50 60 70 80 90 100

DUTY CYCLE

(%)

3509 G14

3509fc

5

LT3509_15

LT3509_15概述

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