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ISO7721: IC can't work , short-circuit between TX and GND,

Betty Guo
Expert 7300 points
Part Number: ISO7721

Hello

my customer test the ISO7721 and face a issue that IC can't work and can't resumed after restart. Test the VCC and TX point,find that short -circuit between VCC and GND also short-circuit between TX and GND. 

At the same time, Is 0.1uF capacity of place at VCC pin effect only for decoupling？

Thanks

  • 0
    TI__Intellectual 2900 points
    Hi Betty,

    Could you please elaborate on what kind of testing was done on the ISO7721 which caused this failure? It would help us understand why the device is behaving unexpectedly.

    Yes, the 0.1uF on the VCC pin is only for decoupling purpose. We recommend having the decoupling capacitor very close to the IC supply pin to get the best performance out of the device. Please refer to Section 11 of the datasheet for additional layout guidelines.

    Regards,
    Anand Reghunathan
  • 0 in reply to Anand Reghunathan
    TI__Expert 7300 points
    Hi Anand,

    thanks for your reply. because customer is sensitive with project information, I can't provide schematic and detail things. The main issue as below:
    1. power on, input current is large 50mA than normal value, IC can't work and short-circuit between VCC and GND.
    2. power on, input current is large 50mA than normal value, IC can't work and only once IC work after restart.
    3. IC output can't follow input signal, main manifestation is input is low , output error trigger.
    next component of ISO7721 is SCM4201A, which is a half duplex enhanced transceiver for RS485.
    Thanks!