Features and Benefits

  • Converts Positive Voltage to Negative Voltage
  • Low Operating Current—100µA
  • Compact 8 Pin MiniDIP and SO Packages
  • High Efficiency—85% Typical
  • Low Battery Detector
  • 4% Output Voltage Accuracy (MAX634)
  • +3V to +16.5V Input Voltage Range
  • Adjustable Output Voltage
    • Up to -20V with Simple Coil
    • Virtually Unlimited Voltage with Transformer

Product Details

Maxim’s MAX634 and MAX4391 CMOS DC-DC regulators are designed for simple, efficient, inverting DC-DC converter circuits. The MAX634 and MAX4391 switching regulators provide all control and power handling functions in a compact 8 pin package: a 1.25V bandgap reference, an oscillator, a comparator for output voltage regulation, and a 525mA P-channel output MOSFET. A second comparator is also provided for convenient low battery detection.

The operating current is typically 100µA and is nearly independent of output switch current and duty cycle, thus ensuring high efficiency even in low power battery operated systems. Operating in the inverting configuration, the MAX634 and MAX4391 can convert a positive input voltage in the range of +3V to 16.5V to any negative output voltage up to -20V.

These devices are pin compatible enhancements of the Raytheon bipolar circuit, RC4391. Improvements include significantly higher efficiency, extended low voltage operation and improved output voltage accuracy (MAX634).

Maxim manufactures a broad line of DC-DC converters, including the MAX635, MAX636, and MAX637; which reduce the external component count in fixed -5V, -12V, and -15V output DC-DC converter circuits. See Table 2 on the last page of this data sheet for a summary of other Maxim DC-DC converters.


  • +5V to ±12V or ±15V Power Conversion
  • Board Level, Local Power Supply Generation
  • High Efficiency Battery Powered DC-DC Converters
  • Regulated Negative Output Power Supplies
  • Regulated Voltage Inverters