MAX660: A Stable Power Inverter
One of the notable integrated circuits from Maxim is the MAX232, renowned for its role as a serial port level shifter, incorporating an integrated charge pump and eliminating the need for an external inductor. A similar design concept has been implemented in the MAX660, which offers a more stable output voltage and higher efficiency. This device has the capability to ‘mirror’ any input voltage ranging from 1.5 V to 5.5 V. With a 5 V input, the output typically hovers around -4.7 V when subjected to a load of 100 mA. Its efficiency stands at approximately 96% at 10 mA and around 88% at 100 mA. In idle mode, with an open-circuit output, the IC consumes an impressively low quiescent current of only 120 pA.
Circuit Configuration and Components
The circuit configuration is relatively straightforward. A 0 Ω resistor on pin 1 selects the operating frequency, functioning at 80 kHz with R1 installed and dropping to 10 kHz without it. The combination of 1:1 and C5 works to minimize ripple on the output voltage. Unlike in a switching circuit, the choice of the inductor is not highly critical. Gerber files for the printed circuit board, which integrates some surface-mount components, can be conveniently downloaded from the Elektor website under the reference 070279-11.zip. Noteworthy SMD components include R1, C1, and C4 in 0603 packages, while C3 is an SMD tantalum electrolytic capacitor. The MAX660CSA or the MAX660M, both available in SO8 packages, can be used interchangeably. Additionally, L1 is a 10 μH SMD inductor rated at 300 mA.