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DRV8824: ESD failure

Faizul Bacchus
Intellectual 1895 points
Part Number: DRV8824

Hello,

My customer is using the DRV8824 motor driver in a 34V application. The motor outputs, AOUT1, AOUT2 and BOUT1, BOUT2 are all connected to a 4 pin connector straight from the driver. The motor then gets plugged into this connector.

The customer is conducting +8kV contact ESD testing on the connector and finding that the DRV8824 are getting damaged. They have tried to fit separately 43V SMA TVS diodes from each of the 4 pins (AOUT1 AOUT2 etc) to ground.

When the diodes are bi-directional ones (SMAJ43) they are not effective and the DRV8824 still fails. When the diodes are unidirectional (SMAJ43A) , it went through the entire test without failure but there were some driver lockouts after some hits. They also observed decay current going through the unidirectional diodes.

They need help to solve the ESD problem for their system and would like to hear all ideas plus an explanation why unidirectional diodes may affect the operation (during decay).

Thanks very much

Faizul Bacchus

  • 0
    TI__Guru** 114905 points
    Hi Faizul,

    We will investigate.

    Can you provide a few additional details?
    Is the system powered when the +8kV contact testing is performed?
    When performing +8kV, where is the negative connected?
    Do all outputs fail? If not, which ones?
  • 0 in reply to Rick Duncan
    Prodigy 170 points

    Hi Rick,

    System is powered up when ESD contact test was done. Test is done while board is installed in the unit (big grounded metal box). ESD gun ground was connected to chassis GND - same potential as board GND.

    With bidirectional 43V TVS AOUT failed on second -8kV hit (we haven't tried -8kV on BOUT). It passed +8kV on both outputs.

    With unidirectional 43V TVS board is passing both +/- 8kV. We are planning to keep these TVSs in design.

    My main question/concern is impact of forward biased diodes in parallel with low side FET body diodes. Based on data sheet there should not be any. In drive current mode (PWM ON) current flow is opposite. In fast and slow decay mode (per Figure 7) appropriate FETs are being turned on and there is no current thru body diodes and TVSs. Correct?

    We figured the reason for occasional lockups after ESD hits. Reset line drive from our uP gets low. Working on fix.

    Regards,

    Darko

         

  • 0 in reply to Darko Hadzidedic
    TI__Guru** 114905 points
    Hi Darko,

    "My main question/concern is impact of forward biased diodes in parallel with low side FET body diodes. Based on data sheet there should not be any. In drive current mode (PWM ON) current flow is opposite. In fast and slow decay mode (per Figure 7) appropriate FETs are being turned on and there is no current thru body diodes and TVSs. Correct?"

    Correct, there should be no impact. In some cases, it may be slightly beneficial. During the dead time, some current may flow through the external diodes and reduce the heat in the device.

    Glad to hear you have found the reason for the occasional lockups.