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UC2842A: OUTPUT pin damaged issue

Vincent Chen64988
Expert 4480 points
Part Number: UC2842A

Hi Team,

My customer has UC2842A output pin damaged issue in their factory. The fail rate is not quite high but they still want to find out the root cause and did some experiments.

Attached are a circuit and a waveform of OUTPUT pin. The supply voltage of  VCC is 17V, the OUTPUT pin has a short spike voltage around 18.96V that might caused by transformer's back EMF. We can found the spike voltage seems to be clamped by ESD diode. Customer wants to know the around 2V spike voltage with 9uS duration will have risk to damage the device or not?

Thanks very much.

Vincent Chen

  • 0
    TI__Mastermind 31580 points
    Hi Vincent,

    I will need to refer this question to an IC designer in the product line. I expect we should have a response within a day.

    Regards

    Peter
  • 0
    TI__Expert 7395 points
    Vincent,
    Thanks for contacting us. Yes, if the gate voltage is higher than Vcc there is risk of damage. I see you say the output of the UC2842A is being measured directly at the pin of the IC. Is the ground connection of the probe being measured at the ground pin of the UC2842A or at the source of the MOSFET or some other place? This signal could depend on measurement technique.

    What topology is this? If there is half-bridge style stacked MOSFETs with both high side and low side, when the low-side switch turns off and the high side switch turns on , the Drain-to-gate capacitance of the low side mosfet can result in pulling the low side switch gate up higher as the high side switch turns on due to fast dV/dt as the drain of the low side switch rapidly rises to the input voltage. You could increase the series resistance to the high side switch to slow its turn-on rate and see if that makes a difference.

    Regards,
    John
  • 0 in reply to John Stevens
    TI__Expert 4480 points

    Hi John,

    The question was asked by component engineer and he cannot disclose too much to us, so I don't know what topology they used, the circuit and waveform I attached are all the information I have now.

    As you mentioned, I will confirm customer's measurement method to see if they already apply the shortest probe loop. I also will ask customer to increase series resistance to the high side switch to see if it help to reduce the overshoot at output pin.

    Thanks very much.

    Best Regards,

    Vincent Chen

  • 0 in reply to Vincent Chen64988
    TI__Expert 7395 points

    Vincent,

    Thanks. Let us know.

    Regards,

    John