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Original question:

DRV8873: Standby current

DRV8873: High standby current and temperature

Sebastian Reinig1
Prodigy 40 points
Part Number: DRV8873

Hi,

in the attached configuration with a DRV8873 I got the problem that some samples take a high standby current of over 50 mA. Some devices only needs the specified current of unter 10mA. The ones with high standby current heats up to about 60°C. What could be the reason for this behaviour?

I tested to control both, a part with high and one with low standby current at the same position on PCB. Over SPI I can contact both devices and even the PWM-output seems to work. 

 

Signals:

  • SDO1/SDI2 connected to next driver in a chain of 5 drivers
  • SDI1, connectet to CPU
  • SPI-SCLK, connected to CPU
  • SPI-NSCS, connectet to CPU
  • FR-DI, connectet to CPU
  • FR-PW, connectet to CPU
  • FR-I, connectet to CPU

DISABLE-Pin on GND that output is always enabled.

 

Regards

 

Sebastian Reinig

  • 0
    TI__Guru** 114905 points

    Hi Sebastian,

    There is no apparent reason for this behavior.

    Is the PCB a custom design?
    Was the PCB hand assembled? If so, could there be some shorts on the board?
    What are the input signals and output signals (including nFAULT) of a low current and high current device?

    Can you set the outputs low of a high current device by setting the MODE bits in IC1 to 11b and re-measure the current?

  • 0 in reply to Rick Duncan
    Prodigy 40 points

    Hi Rick,

     

    thank you for your fast answer.

    The PCB is a custom design which is hand assembled. The board has already been checked for shorts.

    The behaviour of the input signals and output signals has been the same for a high current device and a low current device. The signals were:

    • +3V3 on nFAULT
    • GND on DISABLE
    • +3V3 on nSLEEP
    • GND on IN1 and IN2
    • A little over VM on VCP
    • +VM on CPH with voltage peaks of the charge-pump
    • GND on CPL with voltage peaks of the charge-pump
    • +3V3 on nSCS
    • GND on SDI when not active
    • GND on SDO when not active
    • GND on SCLK when not active
    • VM on VM
    • +1V on OUT1 and OUT2
    • GND on SRC
    • GND on IPROPI1 and IPROPI2

    I tried to change the operating mode but it seems like it is not possible when DISABLE is always low. Instead I cut the connection between DISABLE and GND for setting the devices outputs automatically in high-Z when power is switched on. But the behaviour of the standby current hasn’t changed.

     

    Regards

    Sebastian

  • 0 in reply to Sebastian Reinig1
    TI__Guru** 114905 points

    Hi Sebastian,

    Thank you for the measurements. One that stands out is VCP.

    VCP should be ~5V above VM. There will be some ripple on VCP as the charge pump has some hysteresis to limit the max and min voltage when operating.

    Would you please double check the VCP voltage on both good and suspect devices?

    Hopefully this will provide a clue.

  • 0 in reply to Rick Duncan
    Prodigy 40 points

    Hi Rick, 

    Thank you for your responce.

    The high current device is now completley defective and soldered out. For the remaining parts VCP is ~30V. 

    Because the PCB is completely assembled it is difficult to solder back in a high current device. I think the best way ist to do some testing with the ones left. If there will be a new PCB and again some devices with the same behaviour I'll contact you again.

    Best Regards

    Sebastian

  • 0 in reply to Sebastian Reinig1
    TI__Guru** 114905 points

    Hi Sebastian,

    Thank you for the update.

    And please keep us updated if this occurs again.