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EM1402EVM: power failure

yuefeng huang
Prodigy 30 points
Part Number: EM1402EVM
Other Parts Discussed in Thread: BQ76PL455A, EMB1428Q,

The test point TP4 (VIO) was short-circuited with test point T2 (GND). The voltage of TP3 (VP) voltage was about 1.2V and then slowly decreased, which could not be used.

  • 0
    TI__Genius 11480 points
    Yuefeng,

    For a stacked board, the VIO pin must be supplied by the pl455 VP pin. If VIO is pulled to GND, then the pl455 will shut down and you will see RC decay on VP, which you seem to be describing.

    If you are using a single board, VIO should be supplied by the microcontroller or host interface. Again, if this is pulled low then the pl455 will shutdown and you will not have communication to the EMB devices (the SPI interface is bit-banged through the pl455 GPIO).

    I recommend not shorting VIO to GND
  • 0 in reply to David Wiest Jr
    Prodigy 30 points
    Thank you very much for your answer！
    I use the EM1402EVM in a single board mode. I did not short VIO to GND．When the power is off, the resistance between the VIO and GND is only 1.5 ohm.So, I suspect that a chip on the circuit is damaged, such as Bq76pl455a, or emb1428q
  • 0 in reply to yuefeng huang
    TI__Genius 11480 points
    Hi Yuefeng,

    I think you are on the right track - i would look at the schematics (found at TIDA-00817, www.ti.com/.../TIDA-00817) and search for things that could short VIO to GND if damaged. My top guesses would be the pl455, a capacitor, or any FET/Diode parts located on that net.
  • 0 in reply to David Wiest Jr
    Prodigy 30 points
    Hello! David.

    I have look carefully at the schematics of TIDA-00817,and then tested the board.I'm sure there's no problem with the FET, such as Q46 and Q21.The resistance between the VIO pin of PL455 and the ground is lower than the other position.But the demo board is under warranty,I don't dare to solder the capacitors and chips on the board.I guarantee that I didn't do any destructive testing on the board, and I hope it can be replaced.Would you please help me?