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LTC1555/LTC1556

SIM Power Supply

and Level Translator

FEATURES

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Step-Up/Step-Down Charge Pump Generates 5V

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Input Voltage Range: 2.7V to 10V

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3V to 5V Signal Level Translators

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> 10kV ESD on All SIM Contact Pins

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Short-Circuit and Overtemperature Protected

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Very Low Operating Current: 60

µA

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Very Low Shutdown Current: < 1

µA

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Soft Start Limits Inrush Current at Turn-On

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Programmable 3V or 5V Output Voltage

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650kHz Switching Frequency

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Auxiliary 4.3V LDO/Power Switch (LTC1556 Only)

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Available in a 16- and 20-Pin Narrow SSOP

The LTC

level shifting needed for 3V GSM cellular telephones to

interface with either 3V or 5V Subscriber Identity Mod-

ules (SIMs). These parts contain a charge pump DC/DC

converter that delivers a regulated 5V to the SIM card.

Input voltage may range from 2.7V to 10V, allowing

direct connection to the battery. Output voltage may be

A soft start feature limits inrush current at turn-on,

mitigating start-up problems that may result when the

input is supplied by another low power DC/DC converter.

The LTC1556 also includes an auxiliary LDO regulator/

power switch that may be used to power the frequency

synthesizer or other low power circuitry.

Battery life is maximized by 60

µA operating current and

1

µA shutdown current. Board area is minimized by minia-

ture 16- and 20-pin narrow SSOP packages and the need

for only three small external capacitors.

GSM Cellular Telephone SIM Interface

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16

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10

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CIN

RIN

DATA

DDRV

SS

M1

M0

CLK

RST

I/O

5V

±5%

GND

CLK

RST

I/O

GND

0.1

µF

10

µF

LTC1555

3V GSM

CONTROLLER

SIM

2.7V TO 10V

3V

10

µF

1555/56 TA01

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

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SIM Interface in GSM Cellular Telephones

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Smart Card Readers