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LTC1429

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Regulated Negative Voltage from a Single

Positive Supply

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External Clock for Synchronization in Noise

Sensitive Systems

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REG Output Indicates Output is in Regulation

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Low Output Ripple: 5mV Typ

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Can Provide Regulated – 5V from a 3V Supply

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Supply Current: 600

µA Typ

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Shutdown Mode Drops Supply Current to 0.2

µA

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Up to 12mA Output Current

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Adjustable or Fixed Output Voltages

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Requires Only Three or Four External Caps

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Output Regulation: 5%

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Available in SO-8 Packages

The LTC

signed to provide a regulated negative voltage from a single

positive supply and permits clock synchronization in noise

sensitivesystems.TheLTC1429CSoperatesfromasingle3V

to 8V supply and provides an adjustable output voltage from

– 1.25V to – 8V. An on-chip resistor string allows the

LTC1429CS to be configured for output voltages of – 3.5V,

–4V, –4.5V or – 5V. The LTC1429CS8 is optimized for

applications which require a fixed –4V output from a 5V

supply and requires only a single external 0.1

µF flying

capacitor. The LTC1429CS requires one or two external

0.1

µF capacitors, depending on input voltage. Both versions

require additional external input and output bypass capaci-

tors. An optional compensation capacitor at ADJ/COMP can

be used to reduce the output voltage ripple.

Each version of the LTC1429 guarantees output regulation of

5%. The LTC1429 includes an open-drain REG output which

pullslowwhentheoutputiswithin5%ofthesetvalue.Output

ripple is typically as low as 5mV. The LTC1429 requires an

external clock applied to the SYNC/SD for normal operation

and consumes a typical quiescent current of 600

µA. Holding

the SYNC/SD either high or low brings the device into

shutdown and the supply current drops to 0.2

µA. For appli-

cationswhichdon’thaveaclocksignalavailable,theLTC1261

provides the same functionality with an internal oscillator. For

applications which require output ripple below 1mV, see the

LTC1550/LTC1551. The LTC1429CS is available in a 14-pin

SO package and the LTC1429CS8 is available in an 8-pin SO

package.

Clock-Synchronized

Switched Capacitor

Regulated Voltage Inverter

FEATURES

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GaAs FET Bias Generators

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Negative Supply Generators

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Battery Powered Systems

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Single Supply Applications

– 4V Generator with Power Valid

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

1

2

3

4

8

7

6

5

C2

0.1

µF

C1

0.1

µF

*C3

0.001

µF

POWER VALID

5V

5V

C4

3.3

µF

GND

SYNC/SD

COMP

REG

OUT

LTC1429-4CS8

10k

LTC1429 • TA01

*OPTIONAL

0.2ms/DIV

0V

5V

SYNC/SD

0V

5V

POWER VALID

–4V

0V

Waveforms for –4V Generator with Power Valid

LTC1429 • TA02