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DRV8837: Motor driver supply voltage

Part Number: DRV8837

Hi,

I use DRV8837. VM is supplied from USB (5 V). I run small cheap 6V DC motor purchased on eBay. There is 10 uF bulk capacitor for VM supply voltage (max. allowed by USB).

When reversing or braking there are quite big spikes on VM (up to 8 V). I guess that is due to back-EMF. This causes some issues for other devices on my PCB that are powered by the same USB line and of course it is violating USB rules.

Can you please advise something to eliminate the spikes?

Thanks

Martin

  • Martin,

    This is a USB application which allowed only 10uF capacitance.
    Also, when reversing or braking, the extra winding energy is sent back to input which pushed the input voltage up. So, we have to absorb this energy or dump it to a load.
    To absorb it, we can add a zener to clamp it.
    To dump the energy, we have to monitor the voltage level and add a switch to control the current path.

    According to your description, a zener diode to clamp voltage seems a good solution. You can pick a 6.5V zener and add it to the input.
  • Hi Wang Li,
    thank you for your answer.

    Unfortunately, even 6V2 zener is going to clamp the voltage higher that what USB allows.

    Do you have some motor driver or another "smart" IC that can dump the energy from the motor when braking or reversing rotation?

    Martin
  • Martin,

    For motor drive IC, it cannot tell the input voltage rising from the input source or the output side if it doesn't monitor the current flow.
    IC could have OVP function to protect itself, no matter the voltage is driven by the input source or motor side. But, I don't see the IC provides a dummy load control function.

    We have to add a reverse blocking FET to prevent the reverse current back to the USB input.