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TPS3431: Abnormal waveform of WDO

Gary Wang1
Intellectual 350 points
Part Number: TPS3431

Dears,

the customer SCH is as follows: (R108 and C101 are NC)

the abnormal waveform of the WDO pin is as follows: CH1 is WDI, CH2 is WDO.

please help to see what causes it?

thanks.

  • 0
    TI__Genius 12630 points
    Gary,

    Please use either a resistor tied to VDD or a capacitor or leave floating for CWD pin, do not populate both capacitor and resistor. Please check to see if this fixes your watchdog issue. Thanks!

    -Michael
  • 0 in reply to Michael_DeSando
    Intellectual 350 points

    Dear Michael,

    thanks for your reply.

    I'm sorry that I didn't clearly describe it.

    In cusotmer SCH, R108 and C101 are not welded, CWD pin is floating now.

    According to the datasheet, CWD is NC, and SET1 is 1, so the tWD should be 1360ms(MIN), but according to the customer test results, tWD is only about 15mS which should be less than the minimum range that can be set?

    Please help to provide some analysis directions and Suggestions.

    Thanks

  • 0 in reply to Gary Wang1
    TI__Intellectual 1900 points

    Hi Gary, 

    What is the value of the CWD pullup resistor? A weak pull up may be perceived as a floating pin, CWD cannot be left floating it needs to be connected to VDD or GND.  To isolate the issue please connect CWD to GND and measure the watchdog timeout 

    Regards,

    Antony