LM2781

Ultra-Low Ripple Switched Capacitor Voltage Inverter

General Description

The LM2781 is a charge pump that inverts an input voltage

in the range of 1.8V to 5.5V to the corresponding output

voltage of -1.8V to -5.5V. With use of three or four low-cost

external ceramic capacitors, the LM2781 can provide up to

50mA of output current.

The LM2781 operates at a 210kHz typical switching fre-

quency to minimize supply current (0.7mA typ.). Two charge

pumps operate 180˚ out of phase to significantly reduce the

output voltage ripple compared to that of traditional single-

phase charge pump circuits. If larger output ripple can be

tolerated, optional capacitor C2 may be omitted to reduce

the cost and size of the solution. The LM2781 is available in

an 8-pin Micro SMD chip-scale package.

See also: LM2780, a slow clock (12kHz typ) version of this

topology with extremely low supply current.

Features

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Inverts Input Voltage

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Ultra-Low Voltage Ripple and 8

Ω Typical Output

Resistance with Two Flying Capacitors

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Output Resistance of 18

Ω Using One Flying Capacitor

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210kHz (typ.) Switching Frequency

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8-pin micro SMD Package (1.4mm x 1.4mm x 0.5mm)

Applications

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Cellular Phones

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Pagers

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PDAs

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Op-Amp Power Supplies

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Interface Power Supplies

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Handheld Instruments

Typical Application Circuit

20044701

March 2003

© 2003 National Semiconductor Corporation

DS200447

www.national.com