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DRV8704: V5 pin short with GND

Eric Yang66
Prodigy 30 points
Part Number: DRV8704

described as the tittle 

the DRV8704 chip's V5 pin is shorted with GND and the chip is  heating 

the design is: STM32 chip generate pwm ,control the sleep pin-reset pin-CS pin at 3.3V level ,iso7241 is used to translate the 3.3v-level into 5V-level ,3.3v and 5v is isolated by iso7241.

the VM of DRV8704 is 24V.

when i measure the V5 pin ,it drop down to 0v from 5v. cut off power, i found that the V5 pin is short with GND.

i check the circuit and PCB design, no errors found.

so i confused.

if the V5 short with GND ,there maybe shorting pin.i do not find it.the status regsister set is default.

so, i want to ask ,in which case the V5 short with GND? 

  • 0
    TI__Guru 56650 points
    Eric,

    "when i measure the V5 pin ,it drop down to 0v from 5v" Does it mean you have seen 5V initially?
    The adjacent pin of V5 is ground pin. Is it possible you short Pin 5 (ground) and V5 pin (Pin 6) together when you do the measurement?
    After V5 short to ground, would you shut down all input power supplies and measure the resistance from V5 pin to ground to confirm the IC damage?
  • 0 in reply to Wang5577
    Prodigy 30 points

    yes

    i do all the action you mentioned.

    before connect the chip to 24V power,the sleep pin from STM32 is high,the reset pin from STM32 is low.

    but when i connect the 24V power to the chip DRV8704 the sleep pin drop to 0V.

    and then i found that the V5 pin drop down to 0V

  • 0 in reply to Eric Yang66
    TI__Guru 56650 points
    Eric,

    nSleep pin has an internal pulldown resistor. I am not sure how strong the STM32's pull-up resistor is. Would you put 100kohm or 50kohm resistor on STM32 sleep pin before the chip gets 24V power?
    If the STM32 pin is pulled low with that resistor, that tells us STM32 internal pull-up resistor is not strong enough or doesn't have pull-up resistor to keep nSleep pin high.