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DRV8704: DRV8704 Overvoltage

Mickaël Porte
Prodigy 200 points
Part Number: DRV8704

Hello,

We designed a custom board using the DRV8704. The system drives a platform inside a water tank. The platform goes down by activating the motors and goes up with Archimedes' buoyancy. When the platform goes up the Archimedes' buoyancy is regulated by the motors to control the platform speed. The motors are powered by 24V power supply.

When the platform goes up the motors are generating voltage. During one test the DRV8704 "burned", the pin AOUT1 seems to have melted.

A second failure (on another board) melted the AOUT2 pin and transistor connected to B2HS and B2LS burned.


I would like to protect the xOUTy pins.
Here are my questions :
What is the purpose of xOUTy pins ?
Is there a way to protect them from over-voltage ?
Is there a better component to drive motor as actuator and generator ?

Kind regards,

  • 0
    TI__Guru** 114905 points
    Hi Mickaël,

    What is the purpose of xOUTy pins ?

    The xOUTy pins are used to monitor the FET VDS for shorts, and to connect to xHSy to create turn off the high side FETs.

    Is there a way to protect them from over-voltage ?
    Is there a better component to drive motor as actuator and generator ?

    As the motor turns:
    What voltage is created?
    What is the state of the nSLEEP pin?
    What is the state of the inputs?
  • 0 in reply to Rick Duncan
    Prodigy 200 points

    Hi Rick,

    Thank you for the answer.

    After some research I understood that I need to dissipate energy generated by the motor. When the platform goes up the motor is driven with a PWM set to 100% so the energy cannot be dissipate by the H-bridge or the motor internal resistor.

    What voltage is created ?

    When using a 24V power supply with a PWM set to 50%, the voltage across the motor is around 17V instead of 12V. We didn't test with a PWM set to 100% to avoid to burn the driver.

    What is the state of the nSLEEP pin?

    nSLEEP state is 1

    What is the state of the inputs?

    Not sure if it is the question but the driver is in slow decay when the PWM off times.

    Is there a reference schematic for protecting the motor driver against over-voltage ?

    Regards,

    Mickaël

  • 0 in reply to Mickaël Porte
    TI__Guru** 114905 points
    Hi Mickaël,

    At 24V, you should have plenty of margin to add circuitry.

    When the motor is acting as a generator, it is important to keep the voltages at all pins below the absolute maximum.
    This can typically be done by increasing the bulk capacitors or adding some type of clamp.

    Clamps can be zeners, TVS diodes, or active clamps. For your application, set the clamp to limit the VM voltage to protect the rest of the system. For example if the rest of the system can handle VM = 52V, the clamp could be set to 48V.
  • 0 in reply to Rick Duncan
    Prodigy 200 points

    Hi Rick,

    Thank you,

    I looked at some zener diodes I think it could works with few in parallel but I don't know how much watt I need to dissipate. I also found this thread where a customer describes a more robust idea to dissipate power. I will try to adapt his idea to automatically protect against over voltage without the need of an MCU. Does TI have an application note or a reference circuit to do this (It would make thing easier) ?

    Regards,

  • 0 in reply to Mickaël Porte
    TI__Guru** 114905 points
    Hi Mickaël,

    I have searched and not found an application note or reference circuit.

    Using Zener diodes should work in your application. As you mentioned, determining the power dissipation will be key. Have you contacted the motor manufacturer for assistance?
  • 0 in reply to Rick Duncan
    Prodigy 200 points

    Hi Rick,

    Thanks for your search. We will try with Zener diodes, this maybe enough. If  I design a better circuit I will share it in this thread.

    Regards,