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DRV8811: DRV8811 Chip Failure

YUCHEN JIA
Prodigy 10 points
Part Number: DRV8811

Hi,

We are having a DRV8811 based PCB that driving a stepper motor which is used to control valve movement.  Recently we are seeing some PCB failures.  After some debugging and it is found the DRV8811 has been failed due to some reason.  This DRV8811 chip failure is confirmed with a low impedance between VMA/VMB (pin 28/15) and GND (pin 7 or pin 21), and a low impedance between VCC (pin 10) and GND (pin 7 or pin 21). 

In our design, VCC is 3.3V, VMA/VMB is 24V, Vref is set to about 0.65V and Rsense is 0.22Ohm.  This gives a full-scale chopping current of 0.37A and total power consumption of less than 0.3W.  

Just wondering what could cause a failure of this chip because it has overcurrent protection and thermal shutdown.  But we are seeing a real failure of the chip itself rather than shutdown.  Any ideas? Thanks!

Best,

Yuchen

  • 0
    TI__Guru 55555 points

    Yuchen,

    Can you please monitor VMA/VMB and output voltage?  This is a classic over-voltage failure mechanism.  

    Please also share complete schematic including ALL the decoupling on the power supply.

    Regards,

    Ryan

  • 0 in reply to Ryan Kehr
    Prodigy 10 points

    Hi Ryan,

    Glad to know from you that what kind of failure mechanism it is! Will do as you suggested to monitor VMA/VMB.  By output voltage, do you mean the AOUT1/2, BOUT1/2 outputs?

    Below is our schematic, not sure if you can see the pins clearly.  It doesn't allow me to upload a file.  So I just take a screenshot and paste it over here. Hope you can recognize the pins.

    Best,

    Yuchen

  • 0 in reply to YUCHEN JIA
    TI__Guru 55555 points

    Yuchen,

    It looks like your schematic is missing decoupling capacitors on each VM pin (should be placed as close as possible to VM pin with a short connection to GND).  Also, bulk capacitor is also missing.  I have highlighted each in the image below from the datasheet.

    Please see figure 8.2 in the datasheet for a clearer image.

    Regards,

    Ryan

  • 0 in reply to Ryan Kehr
    Prodigy 10 points

    Hi Ryan,

    Thanks again for your comments.  We do have a bulk capacitor in place for the 24V supply but it is of 220uF instead of 100uF in your drawing.  Is this okay? Our board is pretty compact so it is close to the VMA/VMB pins but an extra cap for each of the two pins is better to be present as you suggested.

    BTW, I'm assuming the output voltage monitoring is meant for the AOUT1/2 and BOUT1/2 pins.  Could you confirm?

    Best,

    Yuchen

  • +1 in reply to YUCHEN JIA
    TI__Guru 55555 points

    Yuchen,

    You can monitor the outputs, yes.  I would also monitor VMA/B pins. 

    Regards,

    Ryan