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TRS3222 power supply capacitor connection

Alec James
Prodigy 20 points
Other Parts Discussed in Thread: TRS3222, TRS232

We have a number of TRS3222 RS232 line driver ICs failing in the field (5 failures in a population of 200 running for < 1 year).

We have incorrectly wired the V+ capacitor (0.1uF 50 v ) X7R from pin 3 to Vcc (5v) instead of ground.  Is this likely to cause device failure or should I look elsewhere?

Thanks 

  • 0
    TI__Guru**** 167546 points

    Alec,

    The V+ capacitor can be terminated to either VCC or GND. That will not affect reliability.
    With a 5V VCC the suggest capacitor for V+ is not 0.1uF. Using different capacitors will affect the ripple voltage on V+ and V- (and DOUT too). However, that is not a reliability concern.

    What is the symptom on the failures? It there more than one failure symptom?

  • 0 in reply to Ron Michallick
    Prodigy 20 points

    The sympton is that DOUT1 does not toggle when DIN1 toggles, pins 13 and 17 are both +5v.

    I'm considering that this may be caused by the power cable to our PCB being inserted the wrong way around.  We have a protection diode that protects the PCB but we have not considered that if both the PCB and the device it communicates with share a common ground, and the comm cable has no ground, we will put 24v between the TRS3222 device ground and the TRS232 tx / rx lines. There are a lot of "if"s but I've destroyed a TRS3222 by constructing this schenario. Will speak to our customer to see if this may have happend....

    Thanks for your help

    A