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Original question:

UCC21710-Q1: Impedance of OC pin

UCC21710-Q1: OC protection Detection threshold

Hiroaki Suzuki
Prodigy 10 points
Part Number: UCC21710-Q1

Tool/software:

Hello.

I would like to confirm the Vocth of the OC pin.

Vocth (Detection Threshold) is specified as follows on the data sheet.

Vcoth min 0.63V - max 0.77V

However, when I measured at -20C, it was 0.61-0.63V, which is outside the specifications.

Could you tell me the rason why it is outside the spec.

  • 0
    TI__Expert 6610 points

    Hi Hiroaki-san,

    OC pin is an input pin, Voch threshold is the voltage level needed to trigger FLT. In normal operation condition, OC pin voltage will be < the threshold range so that OC FLT is not triggered.  However when there is short circuit event, the OC FLT will be triggered. So what you are observing is expected.

    Thanks

    Sasi

  • 0 in reply to Sasikala Thangam
    Prodigy 10 points

    Hello Sasi-san.

    thank you for your reply.

    I have a question.

    >However when there is short circuit event, the OC FLT will be triggered. 

    How much OC pin voltage at that time?

    OC FLT was triggered under the threshold level(6.1-6.2V) on our bench.(-20degreeC).

  • 0 in reply to Hiroaki Suzuki
    TI__Expert 6610 points

    Hi Hiroaki-san,

    Thanks for the details. Is it possible for you to share the following waveforms captured during the SC event (Vgs, Vds and OC pin).

    Is the voltage measured close to OC pin? is it on the high side/low side? Is the behavior observed only at cold temp?

    Is the measurement done with high BW probe and Scope channel?

    Looking forward for your inputs.

    Thanks

    Sasi

  • 0 in reply to Sasikala Thangam
    Prodigy 10 points

    Thank you for your reply.

    I would reply for your questions as below.

    >Is it possible for you to share the following waveforms captured during the SC event (Vgs, Vds and OC pin).
    I don't have waveform because I measured it by digital-multimeter.
    I would paste a picture of measurement method.
    Please refer it.

    >Is the voltage measured close to OC pin?
    Yes.

    >Is it on the high side/low side?
    Both side.

    >Is the behavior observed only at cold temp?
    Yes.

    >Is the measurement done with high BW probe and Scope channel?
    I didn't use Scope.

  • 0 in reply to Hiroaki Suzuki
    TI__Expert 6610 points

    Hi Hiroaki-san,

    The OC spec varies between 0.63 and 0.77, the variation is due to  part to part difference and mainly due to temperature. The lower value of the spec is at cold temp.

    Are you turning on the supply on and off to go to the specific target value? Is there any overshoot involved/?  The value at which it triggers seems close to the lower limit due to temperature and if there are any spike or accuracy issue with measurement/source, it may show at the triggering at the spec limit or lower and with the DMM you can not capture it.

     You will need to capture with high BW probe and Scope and also use precise power supply as the failing value is very close to the spec limit.

    Hope it helps.

    Thanks

    Sasi

  • 0 in reply to Sasikala Thangam
    Prodigy 10 points

    Hi Sasi-san.

    Thankyou for your reply.

    >Are you turning on the supply on and off to go to the specific target value? Is there any overshoot involved/?

    There may have been any overshoot when input voltage was increased.

    I will check about it.

    Thanks.

    Hiroaki