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Maxim > Design Support > Technical Documents > Application Notes > Interface Circuits > APP 836
Keywords: RS-232, rs232, transceivers, EIA/TIA-232, low-voltage operation, 1.8V operation, 3V only, 5V
only, charge pump, single supply, +/-12V supply, +12/+5V supply
APPLICATION NOTE 836
Selecting and using RS-232 Interface Parts for
Your Power Supply Voltages
Jan 01, 2001
Abstract: Devices and circuits are described for RS-232 interfaces operating from a wide range of power
supplies. Systems are described for operation with the traditional triple supply of +5/12/-12V, +5/+12V,
+5V only, +3V to +5.5V only, +2.7V to +3.6V only, and +1.8V to +4.25 for battery operation.
Power Supplies
RS-232-compliant parts need a minimum of two supply voltages, one that is greater than +5V and one
that is less (more negative) than -5V. These two supplies are needed to guarantee the minimum ±5V
output swings required for the transmitters. See Figure 1. In systems that already have ±12V, this isn't a
problem. However, in systems being designed today, ±12V (or other voltages) aren't usually available. To
solve this problem, Maxim has designed a wide array of parts that can be powered from a single supply
by including power-supply converters built directly onto the IC.
Figure 1. RS-232 transmitters must swing at least ±5V. This means that they must be powered with
supplies ±5V.
The following sections describe different power-supply options.
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