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DRV8701: TVS diodes on motor's terminals

Fabrizio Frigeni
Prodigy 50 points
Part Number: DRV8701

Hello,

I am using the DRV8701 to control an H-bridge. The power supply is a 24V battery and the motor's stall current is about 200A.

I need to include TVS diodes at the motor's terminals to get the product certified. Now, my question is how high should the TVS breakdown voltage be to avoid problems with the DRV8701 and with the FETs.

I was thinking of a 28V breakdown because the full-charged battery will be higher than 24V and I don't want the TVS to conduct at normal operation. However, their clamping voltage goes up to 45V, which should be ok for the DRV8701, but is higher than the Vds of the FETs (40V). Is this going to be a problem because the FETs will breakdown before the TVS? Should I change to 50V or 60V Vds FETs?

Thanks!

  • 0
    TI__Guru** 114905 points

    Hi Fabrizio,

    The question of raising the Vds of the FET should be addressed to the FET manufacturers.

    As you pointed out, the DRV8701 should be ok.

  • 0 in reply to Rick Duncan
    Prodigy 50 points

    Hello Rick,

    Yes, I will address that question to the FET manufacturers.

    Just one more doubt: is the DRV8701 going to take care of the voltage spikes from the motor's inductance, or is the TVS going to absorb them? That makes the sizing of the diodes critically different because the motor is likely to carry much more peak power than the typical ESD spike.

    Thanks!

  • 0 in reply to Fabrizio Frigeni
    TI__Guru** 114905 points

    Hi Fabrizio,

    As the voltage spikes, the body diodes of the FETs activate causing the capacitors on VM to absorb these spikes. Typically, if the capacitors are close to the FETs and large enough, the voltage rise can be minimized.

    The TVS diodes should be able to carry the current once acitivated.