ADM3252: Detecting the cable connection

Document created by analog-archivist Employee on Feb 23, 2016
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The RS232 protocol defines a logic 0 as +3 to +15V & a logic 1 as -3 to -15V.
We require to detect when the cable is connected and power up ADM3252E
otherwise switch the power OFF. How do we differentiate between a disconnected
cable and an inactive DTE (not sending data ) to implement the power save
feature?

 

This is actually pretty tricky to do and definitely not straightforward. In one
approach you'd need to use a comparator on the isolated RS-232 side, that would
detect when the RS-232 line is idling, and signal back to the primary side that
a cable is connected.  You'd need to power the comparator and an
iCoupler/opto-coupler channel on the isolated side from the RS-232 lines
themselves, which could be problematic from a current requirement point of
view. 

When a cable isn't connected, the default state of the coupler output would
have to indicate that nothing is connected.  Connecting a cable would then
power up the comparator, and signal that a cable had been connected.

An alternative approach might be to periodically enable the ADM3252E power, and
check for any RX bus activity, and if so, keep the power on to listen for
additional bus communications.

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