1

LT1738

1738fa

The LT

to lower conducted and radiated electromagnetic interfer-

ence (EMI). Ultralow noise and EMI are achieved by

controlling the voltage and current slew rates of an exter-

nal N-channel MOSFET switch. Current and voltage slew

rates can be independently set to optimize harmonic

content of the switching waveforms vs efficiency. The

LT1738 can reduce high frequency harmonic power by as

much as 40dB with only minor losses in efficiency.

The LT1738 utilizes a current mode architecture opti-

mized for single switch topologies such as boost, flyback

and Cuk. The IC includes gate drive and all necessary

oscillator, control and protection circuitry. Unique error

amp circuitry can regulate both positive and negative

voltages. The internal oscillator may be synchronized to

an external clock for more accurate placement of switch-

ing harmonics.

soft-start, output current limit, short-circuit current limit-

ing, gate drive overvoltage clamp and input supply

undervoltage lockout.

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Greatly Reduced Conducted and Radiated EMI

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Low Switching Harmonic Content

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Independent Control of Output Switch Voltage and

Current Slew Rates

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Greatly Reduced Need for External Filters

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Single N-Channel MOSFET Driver

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20kHz to 250kHz Oscillator Frequency

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Easily Synchronized to External Clock

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Regulates Positive and Negative Voltages

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Easier Layout Than with Conventional Switchers

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Power Supplies for Noise Sensitive Communication

Equipment

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EMI Compliant Offline Power Supplies

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Precision Instrumentation Systems

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Isolated Supplies for Industrial Automation

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Medical Instruments

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Data Acquisition Systems

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

Ultralow Noise 5V to 12V Converter

3

10

11

13

SHDN

CAP

NFB

LT1738

GND

17

14

2

GCL

SS

V5

SYNC

GATE

5

1

6

7

8

16

15

12

CS

4

PGND

20

FB

9

5pF

Si9426

10nF

1.5k

3.3k

25k

25k

3.3k

16.9k

1.3nF

22nF

0.22

µF

21.5k

2.5k

10

µH

OPTIONAL

150

µF

OSCON

4

× 150µF

OSCON

12V

1A

MBRD620

5V

100

µF

P3

22

µH

1738 TA01

+

+

+

A

B

25m

Ω

12V Output Noise

(Bandwidth = 100MHz)

400

5

µs/DIV

1738 TA01a

Slew Rate Controlled

Ultralow Noise DC/DC Controller

APPLICATIO S

FEATURES

TYPICAL APPLICATIO

DESCRIPTIO

POINT

B

ON SCHEMATIC

50mV/DIV

POINT

A

ON SCHEMATIC

500

µV/DIV