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DRV8434A: Back-EMF is applied to the output pins by mistake

Shunsuke Yamamoto
Expert 7641 points
Part Number: DRV8434A

Hi experts,

1. Without VCC and VM is not connected to the power supply, what will it happen if the voltages apply to the output pins(AOUT pins and BOUT pins)? For example, the user mistakenly turns the motor and applies Back-EMF on output pins.

2. When the driver is disabled by ENABLE pin, what will it happen if the voltages apply to the output pins(AOUT pins and BOUT pins)? The example situation is same as first question.

3. When the driver is in sleep mode by nSLEEP pin, what will it happen if the voltages apply to the output pins(AOUT pins and BOUT pins)? The example situation is same as first question.

Best regards,

Shunsuke Yamamoto

  • 0
    TI__Mastermind 44135 points

    Hi Yamamoto-san,

    For all three scenarios the BEMF generated will be presented to VM and GND via the body diodes of the output FETs. BEMF generated will be a sine wave. Body diodes act like a bridge rectifier. 

    1. The VM and GND will receive the BEMF voltage. The body diodes will only allow positive to VM and negative to GND. No damage to the driver will happen as long as the generated voltage does not exceed absolute maximum voltage. This is true for all stepper drivers driven with MOSFETs because body diodes are a part of the MOSFET. If there are other electronics powered by VM they will also receive power via this rail. 

    2, & 3. Usually this BEMF generated does not carry a lot of power and does not have the ability to over power the VM voltage rail. If the BEMF is sufficiently high it is possible to pump up the VM voltage if the stepper was spun at a high speed. Similar limits apply as in #1 with absolute maximum ratings of the stepper driver.

    Regards, Murugavel

  • 0 in reply to Murugavel4637
    TI__Expert 7641 points

    Hi Murugavel-san,

    Thank you for answering my question. 

    "as long as the generated voltage does not exceed absolute maximum voltage. "

    Do you mean the absolute maximum voltage on this sentence is the absolute maximum rating of VM, which is 50V in case of DRV8434A?

    Best regards,

    Shunsuke Yamamoto

  • +1 in reply to Shunsuke Yamamoto
    TI__Mastermind 44135 points

    Hi Yamamoto-san,

    "Do you mean the absolute maximum voltage on this sentence is the absolute maximum rating of VM, which is 50V in case of DRV8434A?". Yes, this is correct. Please also pay attention to other components voltage ratings on this VM bus including electrolytic capacitors. Thanks.

    Regards, Murugavel