APPLICATION NOTE 4417

Transceiver IC Generates ±30V

By: Nick Allen-Rowlandson

Abstract: This application note explains how an RS-232 transceiver and a few external components can be combined to generate supply rails up to ±30V. The MAX202 transceiver is featured in the design.

This design idea appeared in the July 20, 2006 issue of Electronic Design magazine.

When applications require only a few millamps of supply current, an RS-232 transceiver IC (here, the MAX202) and a few external components can generate bipolar supply rails up to ±30V. This capability is useful in ±15V op-amp circuits that provide, for example, meter drive, LCD bias, and gas-detector bias.

In the standard application for which it was designed, the internal charge pump of the MAX202 generates ±10V for driving an RS-232 line. In Figure 1 the IC's transmit section drives an external charge pump that generates up to ±30V. Modifications allow the circuit to generate other voltages, such as ±20V. With the addition of external linear regulators it can produce ±15V for bipolar op-amp circuits.

Figure 1. This RS-232 transceiver drives an external charge pump, which provides ±30V supply voltages at a few milliamps.
Figure 1. This RS-232 transceiver drives an external charge pump, which provides ±30V supply voltages at a few milliamps.

The maximum operating frequency for the external charge pump is approximately 120kHz, so a JK flip-flop (or other divide-by-2 circuit connected between +5V and ground) is inserted in the oscillator line to lower the frequency applied to the pump. Lower voltages can be obtained (±20V, for example) by connecting the anode of D1 and the cathode of D2 to ground instead of ±10V.
Next Steps
EE-Mail Subscribe to EE-Mail and receive automatic notice of new documents in your areas of interest.
Download Download, PDF Format
© , Maxim Integrated Products, Inc.
The content on this webpage is protected by copyright laws of the United States and of foreign countries. For requests to copy this content, contact us.
APP 4417:
APPLICATION NOTE 4417,AN4417, AN 4417, APP4417, Appnote4417, Appnote 4417