1

LT1931/LT1931A

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Fixed Frequency 1.2MHz/2.2MHz Operation

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– 5V at 350mA from 5V Input

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–12V at 150mA from 5V Input

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Uses Small Surface Mount Components

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Wide Input Range: 2.6V to 16V

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Low Shutdown Current: <1

µA

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Low Profile (1mm) ThinSOT

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Pin-for-Pin Compatible with the LT1611

The LT

inverting SOT-23 current mode DC/DC converters. Both

parts include a 1A integrated switch allowing high current

outputs to be generated in a small footprint. The LT1931

switches at 1.2MHz while the LT1931A switches at 2.2MHz.

These high speeds enable the use of tiny, low cost

capacitors and inductors 2mm or less in height. The

LT1931 is capable of generating – 5V at 350mA or –12V

at 150mA from a 5V supply, while the LT1931A can

generate –5V at 300mA using significantly smaller induc-

tors. Both parts are easy pin-for-pin upgrades for higher

power LT1611 applications.

The LT1931/LT1931A operate in a dual inductor inverting

topology that filters both the input side and output side

can be achieved when ceramic output capacitors are used.

Fixed frequency switching ensures a clean output free

from low frequency noise typically present with charge

pump solutions. The low impedance output remains within

1% of nominal during large load steps. The 36V switch

The LT1931/LT1931A are available in the 5-lead ThinSOT

package.

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Disk Drive MR Head Bias

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Digital Camera CCD Bias

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LCD Bias

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GaAs FET Bias

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Local Low Noise/Low Impedance Negative Supply

1.2MHz/2.2MHz Inverting

DC/DC Converters in ThinSOT

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

Figure 1. 5V to –5V, 350mA Inverting DC/DC Converter

5V

–5V

350mA

1931 F01

SW

L1A

10

µH

L1B

10

µH

D1

GND

LT1931

C1: TAIYO YUDEN X5R JMK212BJ475MG

C2: TAIYO YUDEN X5R LMK212BJ105MG

C3: TAIYO YUDEN X5R JMK325BJ226MM

D1: ON SEMICONDUCTOR MBR0520

L1: SUMIDA CLS62-100

C1

4.7

µF

C3

22

µF

C2

1

µF

R2

10k

R1

29.4k

C4

220pF

NFB

SHDN

LOAD CURRENT (mA)

0

50

55

65

70

75

100

85

100

200

250

1931 TA01

60

90

95

80

50

150

300

350

Efficiency

FEATURES

DESCRIPTIO

APPLICATIO S

TYPICAL APPLICATIO

ThinSOT is a trademark of Linear Technology Corporation.