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WEBENCH® Tools/DRV8801: quiescent current in sleep mode vs. nFault Output state

Kai Roeben
Prodigy 40 points
Part Number: DRV8801

Tool/software: WEBENCH® Design Tools

Hi Team,

 

we use the DRV8801 to drive a DC motor.

Implementation according to datasheet “DRV8801” (SLVS855J –JULY 2008–REVISED MARCH 2015) page 16.

 

Now, we have assembled 35 pcbs.

Only appox. 25% pcbs shows this strange behavior:

In Sleep mode the nFault output falls slowly to zero voltage / GND and so the quiescent current rises approx. 500µA,

because of the pull up resistor (10k) to V_MCU (5V).

 

But the other pcbs work good - no quiescent current problem.

 

Is this normal? What can we do to reduce the quiescent current in sleep mode?

 

Thanks in advance!

 

Best regards,

 

Kai

  • 0
    TI__Guru** 114905 points
    Hi Kai,

    Please see the post: e2e.ti.com/.../1718078

    When the device enters sleep mode, the nFAULT output is unpredictable. Section 9.3.8 of the datasheet also states this.

    To work around this, it is recommended to use a pullup resistor that can be disabled during sleep. Can the nFAULT GPIO change from a pullup to a pulldown when entering sleep?
  • 0 in reply to Rick Duncan
    Prodigy 40 points
    Hi Rick,

    thank you for your quick answer!!!
    Sorry, I didn’t found directly the responsible post in the forum.

    The work around is possible - thanks!
    But currently we have implemented for the zero series an external pull-up resistor (according to the datasheet).
    Also, our first pcb samples worked good (respective to quiescent current) including all validation and approval tests.

    Now, we’ve to change the assembling to the series and unfortunately we lost time.

    It's a pity that such important information is not realy included in the data sheet.
    Neither in the newer datasheet from the DRV8801-Q1.

    Thank you for your support!

    Regards,

    Kai