LM2780 Ultra-Low Ripple Switched Capacitor Voltage Inverter
March 2003
LM2780
Ultra-Low Ripple Switched Capacitor Voltage Inverter
General Description
The LM2780 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 LM2780 can provide up to
50mA of output current.
The LM2780 operates at a 12kHz typical switching fre-
quency to minimize supply current (60碌A typ.). Two charge
pumps operate 180藲 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 LM2780 is available in
an 8-pin Micro SMD chip-scale package.
See also: LM2781, a fast clock (210kHz typ) version of this
topology with even lower output voltage ripple.
Features
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Inverts Input Voltage
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Ultra-Low Voltage Ripple and 8鈩?Typical Output
Resistance with Two Flying Capacitors
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Output Resistance of 18鈩?Using One Flying Capacitor
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12kHz (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
Pagers
PDAs
Op-Amp Power Supplies
Interface Power Supplies
Handheld Instruments
Typical Application Circuit
20044601
漏 2003 National Semiconductor Corporation
DS200446
www.national.com
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