LM2781 Datasheet, PDF (1/7 Pages) National Semiconductor (TI) – Ultra-Low Ripple Switched Capacitor Voltage Inverter

March 2003
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
n Inverts Input Voltage
n Ultra-Low Voltage Ripple and 8Ω Typical Output
Resistance with Two Flying Capacitors
n Output Resistance of 18Ω Using One Flying Capacitor
n 210kHz (typ.) Switching Frequency
n 8-pin micro SMD Package (1.4mm x 1.4mm x 0.5mm)
Applications
n Cellular Phones
n Pagers
n PDAs
n Op-Amp Power Supplies
n Interface Power Supplies
n Handheld Instruments
Typical Application Circuit
20044701
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