Switched Capacitor Voltage Inverter with Shutdown

Features

• Operating Voltage Range of 1.15 V to 5.5 V

• Output Current Capability in Excess of 50 mA

• Low Current Consumption of 67 A

• Power Saving Shutdown Input for a Reduced Current of 0.4 A

• Operation at 12 kHz • Low Output Resistance of 26

• Space Saving TSOP−6 Package

• Pb−Free Package is Available

Typical Applications

• LCD Panel Bias • Cellular Telephones • Pagers

• Personal Digital Assistants • Electronic Games

• Digital Cameras • Camcorders

• Hand Held Instruments 6

The MAX1720 is a CMOS charge pump voltage inverter that is designed for operation over an input voltage range of 1.15 V to 5.5 V with an output current capability in excess of 50 mA. The operating current consumption is only 67 A, and a power saving shutdown input is provided to further reduce the current to a mere 0.4 A. The device contains a 12 kHz oscillator that drives four low resistance MOSFET switches, yielding a low output resistance of 26 and a voltage conversion efficiency of 99%. This device requires only two external 10F capacitors for a complete inverter making it an ideal solution for numerous battery powered and board level applications. The MAX1720 is available in the space saving TSOP−6 package.

DETAILED OPERATING DESCRIPTION

The MAX1720 charge pump converter inverts the voltage applied to the Vin pin. Conversion consists of a two−phase operation (Figure 15). During the first phase, switches S2 and S4 are open and S1 and S3 are closed. During this time, C1 charges to the voltage on Vin and load current is supplied from C2. During the second phase, S2 and S4 are closed, and S1 and S3 are open. This action connects C1 across C2, restoring charge to C2.

Table 1. Output Resistance vs. Capacitance (C1 = C2 = C3), Vin = 4.75 V and Vout = −4.0 V