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DRV8835: Regarding Vm and vcc

Manali Durgule
Prodigy 95 points
Part Number: DRV8835

Hello sir,

Which power supply is given to the GATE of the MOSFETs of H-bridge, motor supply or Vcc?  When the motor supply reduces to zero will the MOSFETs be in working condition? 

  • 0
    TI__Mastermind 37683 points

    Hello Manali,

    Which power supply is given to the GATE of the MOSFETs of H-bridge, motor supply or Vcc?

    I am researching this and will get back to you by Friday 13th.

    When the motor supply reduces to zero will the MOSFETs be in working condition?

    As long as the VCC is above the UVLO threshold, the MOSFETs will be operational. 

  • 0 in reply to Pablo Armet
    TI__Mastermind 37683 points

    Hello Manali,

    I am currently still researching. I will give you a reply by Wed. 18.

  • 0 in reply to Pablo Armet
    TI__Mastermind 37683 points

    Hello Manali,

    Sorry for late reply.

    Internally, the DRV8835 uses a combination of the motor supply voltage and VCC to drive the MOSFET.

  • 0 in reply to Pablo Armet
    Prodigy 95 points

    Hello sir,

    I was testing DRV8835 in Phase/Enable mode. A ENABLE, A PHASE and MODE were high. So Aout2 was high. 

    Vcc given was 5 V. I reduced VM from 4.2 V to 0 V gradually. Simultaneously, I was checking for short circuit between Aout1 and ground. As Aout2 is high, Aout2 was expected to be connected to the ground. 

    When I reached to the voltage of 1.3 V, Aout1 was disconnected from ground. It was not connected to the ground till the VM was reduced to 1V. Hence for the band of 1.3 V to 1 V, Vout1 was not disconnected from ground. When I reduced voltage further from 1 V to 0 V, it was again connected to the ground. 

    Vcc was constant throughout the process. 

    After this testing, I kept VM  constant at 5 V and decreased VCC gradually from 5V to 0V. When it reached voltage of 1.3 V. Aout1 was disconnect from ground for the same conditions of A PHASE, A ENABLE and MODE as before. And it remained disconnected from ground till it reached 0V. Hence I guess the internal MOSFETs and logic circuitry turned off after VCC reached 1.3 V. 

    Can you please tell me how is it working exactly? 

    Thanks and regards,

    Manali Durgule 

  • 0 in reply to Manali Durgule
    TI__Mastermind 37683 points

    Hi Manali,

    Thank you for sharing your test results. It is interesting.

    I will contact one of the designers of the device and verify if this is expected behavior. I will post a reply once I hear from the designer. Expect a reply from me by Friday 3rd.

  • 0 in reply to Pablo Armet
    TI__Mastermind 37683 points

    Hello Manali,

    If you read section 9.2 of the datasheet it says "The VM voltage supply does not have any undervoltage lockout protection (UVLO), so as long as VCC > 1.8 V, the internal device logic remains active. This means that the VM pin voltage may drop to 0 V, however, the load may not be sufficiently driven at low-VM voltages."

    In the case where you kept VM constant and dropped VCC, the device internal logic was disabled once the VCC dropped below 1.3V. The 1.8V is the maximum value so that's why you observed the device behaving normally from 1.3V-1.8V. 

    In the case where you kept VCC constant and lowered VM, the load was not sufficiently driven at VM < 1.3V.