Ultra-Low Ripple Switched Capacitor Voltage Inverter
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 frequency 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.
By National Semiconductor Corporation
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