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DS8923A transceiver

Angela Brock
Intellectual 480 points

Hi

I am designing with the DS8923A.  Currently I have a resistive coupling circuit-- with a resistor between the two differential receiver inputs as well as in series on each differential.  What I am wondering and can't seem to locate anywhere is how to determine the values of the resistors.

  • 0
    Intellectual 480 points
    I tried some different values of series resistors with a 10k parallel r. I sent a 3.3V 1kHz square wave differentially to the receiver. I noticed that as the series resistor values increased, the low voltage at the input pins increased while the high voltage stayed near 3.3V. I would expect the input values to decrease unless the chip was outputting voltage at the receiver input on the low level signal. Can someone explain the analysis of this circuit?
  • 0 in reply to Angela Brock
    TI__Mastermind 43795 points

    Angela,

    The receivers have an input resistance to GND of about 6K.  It is unusual to have a series resistance in combination with a parallel resistor across the input pair.  The DS8923 has a fairly wide input common mode range - why do you need the extra resistors?

    Lee