The Maxim MAX634 and MAX4391 are CMOS micropower inverting switching regulators that convert a positive input voltage (3 V to 16.5 V) to a negative output voltage up to –20 V. They integrate a 1.25 V band‑gap reference, oscillator, output MOSFET and low‑battery detector in an 8‑pin package, delivering up to 525 mA peak output current with typical efficiency around 85 %.
The document provides absolute maximum ratings, electrical characteristics, typical operating curves, circuit diagrams, component selection guidelines, and example applications such as –5 V, –12 V and –15 V output converters. It also includes ordering information for the various package options.
| Input voltage range | +3 V to +16.5 V |
|---|---|
| Peak output current | 525 mA |
| Typical efficiency | 85 % (typical) |
| Reference voltage | 1.25 V |
| Oscillator frequency | ~40 kHz (with 47 pF capacitor) |
The devices operate with a positive input voltage from +3 V up to +16.5 V.
Both parts can source up to 525 mA peak output current.
The oscillator uses a single external capacitor; a 47 pF capacitor yields about 40 kHz.
Typical efficiency is about 85 % when using low‑loss inductors.