MAX775

• +3V to +16.5V Operating Range
• Tightly Regulated, -24V Output for Off-Hook Voice Communication
• -70V Output Supports a Five-Ringer-Equivalent Load (VIN > 10.5V)
• Compact Construction
• Proven PC Board Design
• Uses Off-the-Shelf Components
• Up to 84% Efficiency
• 5µA Shutdown Current
• Fully Assembled and Tested

The MAX774 ISDN ring-tone power-supply (IRG) evaluation kit (EV kit) provides the high voltages required for implementing a plain old telephone system (POTS) interface on ISDN modems and line cards. It is a fully assembled and tested board that provides a tightly regulated, -24V output for powering off-hook voice communication and a -70V output for on-hook, ring-tone generation.

The EV kit is designed for applications that implement the telephone interface using subscriber line interface circuit (SLIC) ICs, such as the AM79R79 from AMD and comparable products from Lucent, Harris, and other vendors. Its design feeds back the -24V output, achieving tight regulation for clean voice-signal transmission. An economical, off-the-shelf, surface-mount transformer reduces system cost and size. Compact design conserves board area. High efficiency and reduced quiescent current make this design the optimal solution for green PC and portable designs.

The MAX774 IRG EV kit can also be used to evaluate the MAX775/MAX776. It has a layout that allows modification for -48V output operation as well as adaptation for lower-voltage European applications.

Applications

• Battery-Powered Applications
• Data Communications
• High-Efficiency DC-DC Converters
• LCD Bias Generators