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Maxim > Design Support > Technical Documents > Application Notes > Interface Circuits > APP 1863
Keywords: analog switches, phase reversal switches, MAX4526/MAX4527, power switching, digital signal
switching, differenential data, full-wave rectifying
APPLICATION NOTE 1863
Transmit Digital Signals and Power Over Same
Wires
Jan 31, 2003
Abstract: Analog switches can be used to enable the transmission of digital signals and power over the
same two wires. The signal waveform is rectified at the remote location to provide a stable supply voltage
and modest load current (about 1mA maximum) for the receiver.
This signaling system enables the transmission of digital signals and power over the same two wires
(Figure 1). The signal waveform is rectified at the remote location to provide a stable supply voltage and
modest load current (about 1mA maximum) for the receiver.
Figure 1. This digital signaling system accepts single-ended data, transmits differential data, and
produces a supply voltage for the receiver by full-wave rectifying the remote-end signal.
For conventional single-ended data, a series of "0s" can allow excessive droop in the receiver's supply
voltage. To avoid that problem differential data (±5V to ±18V) is transmitted, pseudo RS-485 style, from
a single-ended logic-level input. The full-wave rectifier and differential drive ensures that a supply voltage
is always present
Current-limiting resistors at the supply inputs prevent damage in the event of a line short. Values of 1kΩ
are optimum. Higher values produce excessive switching noise at the chip side of the resistors, caused
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