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DRV8800 / Short nFAULT output at the edge of nSLEEP

S.Satoshi
Guru 21685 points
Other Parts Discussed in Thread: DRV8800

Hi All,

Now my customer has  evaluated DRV8800 on their evaluation board and then they found the short nFUALT output at the edge of nSLEEP as attached. I'd like to know if this behavior is known operation. And if so, please let me know the typical period of this nFAULT output at both rise and fall edge of nSLEEP.

Best Regards,

Sonoki / Japan Disty

  • 0
    TI__Guru** 114905 points
    Hi Satoshi-san,

    Yes this behavior is expected. nFAULT is signaling that VBB is in undervoltage.

    There is additional information to clarify.

    Please note the datasheet states in the Diagnostic Output section: "This output is not valid when nSLEEP puts the device into minimum power dissipation mode (i.e., nSLEEP is low)." This means nFAULT could be high or low during sleep. If this is an issue, a simple fix to connect a 10k pullup resistor from nSLEEP to nFAULT. This will disable the pullup when the device is in sleep mode.

    I hope this answers your question.
  • 0 in reply to Rick Duncan
    Guru 21685 points

    Hi Rick-san,

    Let me ask one more question.

    Please let me know the duration of asserting Low from nFAULT after nSLEEP Low to High. I found following information from "Low-Power Mode" section in datasheet.

    When switching from low to high, the user should allow a 1-ms delay before applying PWM signals. This time is needed for the charge pump to stabilize.

    So I think that the duration should be within 1msec. Is my understanding correct?

    Best Regards,

    Sonoki

  • 0 in reply to S.Satoshi
    TI__Guru** 114905 points
    Hi Satoshi-san,

    Yes, your understanding is correct. The charge pump stabilizes within 1msec.
  • 0 in reply to Rick Duncan
    Guru 21685 points
    Hi Rick-san,

    Thank you for your quick response !!

    BR,
    Sonoki
  • 0 in reply to S.Satoshi
    Guru 21685 points

    Hi Rick-san,

    Let me ask again about nFAULT low pulse at nSLEEP edge.

    I understand that the short low pulse of nFAULT at nSLEEP edge is expected behavior as you commented before. Customer can see the width of the pulse is approx. 20usec at almost samples, but they found that long pulse >1msec after second nSLEEP edge at only one (1) sample.

    Please give your comment if this is also expected behavior or this sample is suspected to damaged.

    DRV8800 nFAULT low pulse.pdf

    Best Regards,

    Sonoki / Japan Disty 

  • 0 in reply to S.Satoshi
    TI__Guru** 114905 points
    Hi Satoshi-san,

    How much current does the motor require on startup? Please capture the current through the device or the voltage across the Rsense pin when this event occurs.

    Is it possible that this is an overcurrent event? Overcurrent creates a 1.2ms nFAULT pulse.
  • 0 in reply to Rick Duncan
    Guru 21685 points
    Hi Rick-san,

    Now I'm requesting customer to check current. Please let me get back to you.

    Best Regards,
    Sonoki
  • 0 in reply to S.Satoshi
    Guru 21685 points

    Hi Rick-san,

    The overcurrent can not be seen when nSLEEP was changed from Low to High as attached (nSLEEP waveform is not included).

    DRV8800 nFAULT low pulse_Ibb added.pdf

     Host detected error and disable nSLEEP due to longer low duration of nFAULT than normal operation. This may be failure of this sample because this behavior has been confirmed only this sample. Please give your opinion.

    Best Regards,

    Sonoki

  • 0 in reply to S.Satoshi
    TI__Guru** 114905 points
    Hi Satoshi-san,

    My apologies. I was not clear about the current. The current should be measured through the motor when the device is enabled.

    Please ask if there is a capacitor connected to the motor. If there is, what is the value and the tolerance?

    Is it possible to perform a swap of a working part and the suspect part between systems? If the same behavior follows the suspect part to the new system, this will confirm the suspect part. Only the DRV8800 should be swapped. All other components should remain with the system.