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Original question:

DRV8837: Vcc powr supply using 1.8+/-3% DC/DC

DRV8837: 1.8V VCC to drive DRV8837C

Koyo Asaishi
Intellectual 1760 points
Part Number: DRV8837
Other Parts Discussed in Thread: DRV8210P

Hello team,

My customer want to use 1.8V to drive VCC of DRV8837C and I understand UVLO may be enabled when VCC<1.8V from below post.
https://e2e.ti.com/support/motor-drivers-group/motor-drivers/f/motor-drivers-forum/865697/drv8837-vcc-powr-supply-using-1-8--3-dc-dc

I have several questions. This is urgent so kindly answer by today.

  1. Can customer use 1.8V±5% (1.71V-1.89V) after the device exit UVLO?
    Max value of UVLO falling is 1.7V so they can apply this usage after making sure higher than 1.8V is applied.
  2. Customer have tried to apply less than 1.7V VCC gradually but they didn't observe UVLO is suddenly activated but observe output gradually decrease at around 1.3V-1.4V. Vise versa, they observe similar behavior when VCC is increased from low voltage. Is this behavior as your expectation? Please share if you have referenceable waveform.

Best regards,
Koyo

  • +1
    TI__Mastermind 37683 points

    Hi Koyo,

    Koyo Asaishi said:
    Can customer use 1.8V±5% (1.71V-1.89V) after the device exit UVLO?

    1.71V is very close to the 1.7V MAX VCC undervoltage lockout specification. As long as the VCC supply is very stable and there is enough decoupling capacitance to filter out any spikes, UVLO may not be flagged.

    Koyo Asaishi said:
    Customer have tried to apply less than 1.7V VCC gradually but they didn't observe UVLO is suddenly activated but observe output gradually decrease at around 1.3V-1.4V. Vise versa, they observe similar behavior when VCC is increased from low voltage. Is this behavior as your expectation? Please share if you have referenceable waveform.

    There will be some hysteresis around 1.7V. Therefore, UVLO will not trigger right when the VCC voltage drops below 1.7V. What the customer is observing is expected. 

    Regards,

    Pablo Armet 

  • 0 in reply to Pablo Armet
    TI__Intellectual 1760 points

    Hello Pablo,

    Thanks for the prompt answer. It is very helpful.

    So I imagine below picture from your statement. Is my understanding correct?
    I have checked SLVA769A and 1.7V to 1.8V is "Functional" so I want to make sure what peformance can be deteriorated.
    Customer use up to 25mA which is very lower current than maximum drive current. I hope they can use this device without an issue as long as they must keep higher than 1.7V VCC after the device exit UVLO.

    Best regards,
    koyo

  • 0 in reply to Koyo Asaishi
    TI__Intellectual 1760 points

    Hello Pablo

    Can you reply at least what peformance can be deteriorated when VCC is between 1.7V and 1.8V?

    Best regards
    Koyo

  • +1 in reply to Koyo Asaishi
    TI__Mastermind 37683 points

    Hi Koyo,

    Apologies for late reply. It was a holiday yesterday.

    There are no deteriorating performance when VCC is 1.7V to 1.8V. What could happen is the VCC voltage dipping below the UVLO threshold.

    If this is a concern for them, I recommend the DRV8210P as an alternative. It is P2P with the DRV8837C and its UVLO is 1.65V.

    Regards,

    Pablo Armet