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DRV8251A: Will the output current at the OUT end still increase after triggering It rip?

Rhea Gao
Expert 2580 points
Part Number: DRV8251A

Tool/software:

Hi,

When the customer now detects that the OUT1 and OUT2 of the DRV8251A chip are short-circuited, the Itrip of the chip is triggered first, and then the Iocp is triggered. Previously, when other chips were short-circuited, the Iocp was directly triggered. May I ask what causes this current change? Will the output current at the OUT end still increase after triggering It rip?

Thanks~

  • 0
    TI__Expert 4790 points

    Hi Rhea, 

    Thank you for reaching out to us. 

    The OCP triggers if current exceed IOCP (Min:4.1A or  3.7 A ) for longer than tOCP( Typ: 1.5 us). If this analog current limit persists for longer than the OCP deglitch time (tOCP), all FETs in the H-bridge will disable. The driver re-enables after the OCP retry period (tRETRY) has passed. 

    In the capture you shared, the VOUT voltage is high during tOCP value which is not expected behavior in which all FETs in the H-bridge should be disabled. 

    Would you please explain how the short circuit is implemented?

    and also please zoom more into the highlighted zone below to see how long is current period duration. if the tOCP is less than 1.5 us, the OCP is not triggered. 

    Best regards, 

    Mojtaba.

  • 0 in reply to Mojtaba Afshar
    Prodigy 10 points

    Hi, Mojtaba,

    Let me first provide some explanations regarding your questions and this test waveform:
    ① In the above figure, VOUT measures the supply voltage VM, and a 5V power supply is used.
    ② Short-circuit method: Use a small circuit breaker IC65N to short-circuit OUT1 and OUT2.
    ③ The duration of the first-segment current before the short circuit does not meet 1.5 μs. The Itrip voltage value we set is 1.6A. For a more detailed waveform, please refer to the figure below. The first two figures show the waveform when Itrip is triggered at the beginning, and the last two figures show the waveform when Iocp is triggered. 

    My question is: Why isn't Iocp triggered directly after the short circuit? After Itrip is triggered and protection is activated, the current increases and then Iocp is triggered. In previous short-circuit condition tests, Iocp was always triggered directly. I'm very confused about this current change. Please provide an explanation. Thank you.

  • 0 in reply to Gao momo
    TI__Expert 4790 points

    Hi Gao, 

    Thank you for providing the captures.

    Gao momo said:
    My question is: Why isn't Iocp triggered directly after the short circuit?

    The OCP triggers if current exceed IOCP (Min: 3.7 A ) for longer than tOCP( Typ: 1.5 us). If this analog current limit persists for longer than the OCP deglitch time (tOCP), all FETs in the H-bridge will disable.  The provided capture shows that the short circuit does not persist enough to trigger OCP. The capture shows the short circuit time is less than 1.5 us (0.78 us) which is not enough to trigger the OCP. 

    Gao momo said:
    In previous short-circuit condition tests, Iocp was always triggered directly. I'm very confused about this current change. Please provide an explanation

     The Typical value for tocp is 1.5 us however, the min value can be less than 1.5us. This may cause to trigger OCP faster than 1.5us. To better assist, would you please provide us waveform capture. 

    Best regards, 

    Mojtaba.