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DRV8350: Fault Condition Indicator raise as soon as I enable the driver, even with no PWM signal

Part Number: DRV8350

I have a board designed that includes DRV8353RH where everything seems to work fine (buck regulator, VGLS, charge pump) until I pull high the ENABLE pin of the DRV8350. 745us after I pull the ENABLE pin HIGH I can see how the nFAULT pin goes LOW, even before I start sending any control PWM signal (all INLX, INH_X pins = LOW). No matter which PWM Mode I select, I always see the Fault pin to go LOW indicating a fault as soon as I pull the ENABLE pin HIGH (3V3).

Unfortunatelly this is not an SPI version of the chip, so I just have the nFAULT indication of something going wrong. I have reviewed all the possible fault conditions but I do not find the cause in my board:

1/  VM Undervoltage => My VM is 12V, which is well above 8.3V (VVM_UV), so this cannot be the cause

2/ VDRAIN Undervoltage => VDrain = VM = 12V, as VVDR_UV is 6V5 this is not the cause of the fault, too

3/ Charge Pump Undervoltage => VCP is 22V5 when I enable the board, well above 12V+5V = 17V, not the cause too

4/ VGLS Regulator => I measure VVGLS = 12V, above VVGLS_UV = 4.25V, not the cause

For the remaining causes of fault the PWM must be working, but as said I see the Fault before I start sending any PWM signal.

Do you have any recommendation on how can I proceed now to identify what is causing the FAULT?

  • Hi Eduardo - we will check and suggest some ideas for you to proceed. In the meantime
    1. Could you check your board (with a DMM) for any obvious shorts on any of the pins ?
    2. Could you check the voltage on the DVDD pin ?
  • Hi Anuj,
    thanks for your prompt answer.

    The DVDD voltage is 5V when I set ENABLE pin to HIGH (3V3), 0V when the driver is disabled.

    I have checked the board and I could not find any short on any of the pins.
    But when I measure the output impedance between GHB-SHB, between CLB-SLB, between GHC-SHC and between GLC-SHC I find an infinite output impedance in all four, while I think it should be 150K, as I find when I measure the output impedance between GHA-SHA and also between GLA-SLA. Might this indicate that the gate driver blocks for B and C of the DRV8350 are dead on this chip?
  • Hi again Anuj,

    after carefully reviewing the board I discovered that some of the pins had not been properly soldered due to excess of solder on the thermal pad. After reworking, the problem was fixed.

    Thanks for your help.