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DRV8839: Break down after operating normally

Part Number: DRV8839

Hello everyone!

I am currently working on a new PCB design that needs to drive a DC motor in 2 directions. I came across the DRV8839 and I thought it would be a good fit for the motor. For some background, the motor uses 6V and has 1.9A of stall current. I understand the DRV8839 drives up to 1.8A but as the current is limited, I thought it shouldn't be a problem since the running current is 1.1A. Circuit screenshot attached here.

After I got the boards, I tested the motors briefly and they all worked fine, but when endurance testing them, even after 5 minutes of having it turning-breaking-turning, the drivers died. Some of the smoked a bit, some of them just stopped with no physical manifestation. I have been told that having the VCC at 6V and driving the IOs (IN1, IN2 and ENx) at 3.3V with an MCU is not a good idea since it could lead to latch-up. Is this what is happening? Is there anything else I'm missing?

Thank you,

Bruno

  • Hi Bruno,

    The image attached did not appear. Would you please re-send it?

    Also, can you provide a snippet of your schematic showing all connections to the DRV8839?

    In particular, we are interested in bulk capacitors, external components to and from the mcu, external components on the outputs.

    If you have VCC and VM connected together, voltage spikes generated by the motor could be causing the VCC pin to exceed the absolute maximum voltage.
    Please consider this while we await your information.

  • Hi Rick!

    Please see the image below (the top one is the old design that is having issues). The IN1, IN2 and EN signals go straight to the MCU at 3.3V control signal. VMEM is connected to the 6V supply via a 0.1 Ohm shunt resistor to measure current.

    I don't have a bulk capacitor or any components on the output in the old design, which was a design error on my end. I did add those to my next revision (picture at the bottom, not sent to fab yet), as well as 3.3V supply voltage on VCC.

    I want to know if what I am experiencing with the old design will be fixed in the new one, or if there is something else that might be causing the drivers to break.

    Thank you!

    Bruno

  • Hi Bruno,

    Thank you for the additional information.

    In the original design with no bulk capacitor and VM and VCC effectively shorted, it is likely the device was being damaged because the VCC voltage was exceeding the absolute maximum voltage.

    Adding the bulk capacitor and changing VCC to 3.3V should help.

    VCC should now be isolated from any inductive spikes from the motor. As long as VM remains below the recommended max voltage of 11V, there should be no problems.

    You may not need a 100uF bulk cap, but definitely need a bulk. The DRV8839EVM uses a 10uF.

    FYI -- please note that the 1uF capacitor may create an overcurrent condition.

    Please consider lowering the capacitor to 100nF.

  • Hi Rick!

    That's very helpful, thank you. I will change the 1uF capacitor to a 100nF but I'll probably leave the 100uF bulk capacitor as I have a bunch of other ones in the board, meaning the cost difference will be negligible and I will be on the safe side.

    Bruno