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LT1108

Micropower

DC/DC Converter

Adjustable and Fixed 5V, 12V

DESCRIPTIO

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FEATURE

The LT1108 is a versatile micropower DC/DC converter.

The device requires only four external components to

deliver a fixed output of 5V or 12V. Supply voltage ranges

from 2V to 12V in step-up mode and to 30V in step-down

mode. The LT1108 functions equally well in step-up, step-

down, or inverting applications.

The LT1108 is pin-for-pin compatible with the LT1173, but

has a duty cycle of 70%, resulting in increased output

current in many applications. The LT1108 can deliver

150mA at 5V from a 2 AA cell input and 5V at 300mA from

9V in step-down mode. Quiescent current is just 110

µA,

making the LT1108 ideal for power conscious battery-

operated systems.

Switch current limit can be programmed with a single

resistor. An auxiliary gain block can be configured as a low

battery detector, linear post regulator, undervoltage lock-

out circuit, or error amplifier.

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Operates at Supply Voltages from 2V to 30V

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Consumes Only 110

µA Supply Current

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Works in Step-Up or Step-Down Mode

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Only Four External Components Required

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Low Battery Detector Comparator On-Chip

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User Adjustable Current Limit

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Internal 1A Power Switch

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Fixed or Adjustable Output Voltage Versions

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Space Saving 8-Pin MiniDIP or S8 Package

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APPLICATI

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Palmtop Computers

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3V to 5V, 5V to 12V Converters

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9V to 5V, 12V to 5V Converters

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LCD Bias Generators

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Peripherals and Add-On Cards

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Battery Backup Supplies

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Cellular Telephones

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Portable Instruments

APPLICATI

TYPICAL

LOAD CURRENT (mA)

1

78

80

82

84

10

100

LT1108 • TA02

76

74

72

70

AVX

TPS

330

µF

6.3V

L1*

100

µH

LT1108 • TA01

1N5817

5V

150mA

GND

SW2

SW1

LT1108-5

SENSE

100

µF

+

*L1 =

+

2

× AA

CELLS

GOWANDA GA20-103K

COILTRONICS CTX100-4

SUMIDA CD105-101K

47

Ω

Efficiency

Palmtop Computer Logic Supply