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DRV8312: Bootstrap diode for phase B failed

LM
Prodigy 40 points
Part Number: DRV8312
Other Parts Discussed in Thread: INA240

Hi,

I'm seeing some failures of the phase B bootstrap diode on my board with a DRV8312. I believe the diode is failing open - I cannot see a 0.5V diode drop across it anymore.

Phases A and C are OK. I also believe the device is going into BST_UVP (after the failure), as I can see a few drops in voltage in the output waveform where it is trying to charge the bootstrap cap (per 7.3.2.1).

DRV8312 is configured in OC latching shutdown mode (set at 8.1A with 33K resistor), PWM frequency is 30Khz, BST capacitors are 1uF (I have also experimented with 100nF).

My drive is running FOC, and I'm holding the RESET_X pins high while driving the PWM_X pins with a PWM signal. My DC bus voltage is 24V, and my motor has about 150mR of phase resistance.

This working well until I purposefully apply a large current command step to try and push the board into OC to test it's reliability. The DRV8312 does go into OC and I see the bootstrap diode failures after.

I do not have series inductors on the output, although I am measuring phase A and C currents in line with a current sense resistor and INA240.

Does anyone have any advice on an approach to protect against a failure like this?

Is it possible the small amount of inductance in the current sense resistors is saving phases A and C?

Thanks

  • 0
    TI__Mastermind 23950 points

    Hi Laurence,

    1. Could you provide an Oscilloscope capture of the BST_B, OUT_B, and PWM_B so that I may see the drops in the voltage?
    2. Did this problem occur when the bootstrap capacitors were 100nF as well?

    Thank you,

    Joshua

  • 0 in reply to Joshua Horlander Cruz
    Prodigy 40 points

    Hi Joshua,

    Thanks for your reply. Point 2 prompted me to go back and look at my notes. It seems that the board that I installed the 100nF caps on was one that had died - I just had not figured out that it actually was dead at the time I installed the 100nF caps.... So that test was bunk.

    I installed some 100nF capacitors onto a working board and I think this has done the trick. I put the board through 11 over-current events and it is still working well. Previously I was only able to survive 1 - 2 over-current events.

    This was a tricky one to debug. Although the bootstrap diode had failed, DRV8312 behaved almost as if it was a working chip and I actually thought I had a software error for a while. I was still seeing output on phase B, it just looked a little strange and it wasn't until I actually probed BST_B that I discovered that its voltage was not sitting above the phase B voltage, rather at the same voltage. If you would still like the oscilloscope shots I can send them through, otherwise we can close this off.

    Thanks again for your help.

    Laurence M