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Original question:

DRV8850: No output

DRV8850: Failure of driver and high current draw after switching between motors during test

David Smith10
Prodigy 30 points
Part Number: DRV8850

Hello, my name is Dave

I have a question about the DRV8850 for which I have been trying to get an answer.

We're using the 8850 highly leveraged from the TI design and have had 3 of 20 fail in a short period of time

We know that there is internal short detection that protects the chip so we are concerned that we have done something wrong

Our first 20 boards were hand assembled and there were a few that had bad solder joints so we know there is an issue there

I saw that someone was having trouble with shorted parts but didn't see a remedy

We have a procedure for programming

Our process to program the controller (with connections to the output disconnected) is to connect the programmer to the board, plug the USB cable in to the laptop, turn on the 5V power to the board and then program. Then connect to the motor and it runs properly, power down, connect to a different motor and the 3A power supply goes into overcurrent, the chip doesn't get hot but the board is dead.

Subsequent powerup of the board doesn't crowbar the supply but the board has 1 amp current draw and the chip starts to heat rapidly.

I tried to contact Rick Duncan re:e2e.ti.com/.../843770 because it looked like a similar issue... If you don't understand perhaps you can give me an email for Rick that works and he probably will.

 

  • 0
    TI__Guru** 114905 points

    Hi David,

    Looking back at the information provided show the operating voltage is 5.4V. If the DRV8850 VCC voltage spikes much higher, this could violate the absolute maximum voltage of the device.

    Have you looked for voltage spikes during your testing to see the maximum voltage on VCC?

  • 0 in reply to Rick Duncan
    Prodigy 30 points

    Rick,

    I did note that the supply voltage goes above 7V when I cut power to the motor while it is running and not at any other time. If I don't cut power but instead unplug the supply it doesn't appear to have the same issue. Obvious choices are to not cut the power to the board and instead cut power to the supply or clamping the supply voltage. Is there a preferred solution that is recommended in these situations?

    Thanks,

    Dave

  • 0 in reply to David Smith10
    TI__Guru** 114905 points

    Hi Dave,

    The choice will depend on your final application.

    It sound like you are performing some type of testing, and can avoid voltage spikes by changing the procedure.

    In the final application, can you experience a similar voltage spike? If so, then some type of protection may be required.

    This protection could be increasing the bulk capacitor, adding a TVS on the VCC pin to clamp the voltage, or a combination of the two.

  • 0 in reply to Rick Duncan
    Prodigy 30 points

    Rick,

    Thanks for the help.

    Dave