• State Resolved
  • Locked Locked
  • Replies 6 replies
  • Answers 2 answers
  • Subscribers 30 subscribers
  • Views 205 views
  • Users 0 members are here
Support feedback
Options
Options
Similar topics

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

DRV8876: Connecting 2 motors through relays

Oba
Genius 15770 points
Part Number: DRV8876

Hello,

In my customer’s system, there are 2 motors and they want to connect 1 DRV8876 to these 2 motors by using relays like the below.
Because they don’t use them simultaneously and MCU doesn’t have enough GPIOs to connect 2 DRV8876s.

 

Is there any concern for this usage?

 

Regards,

Oba

  • 0
    TI__Mastermind 37683 points

    Hi Oba,

    I don't see any obvious issues with this implementation. As long as the output current remains below the OCP threshold and the power dissipation through the relay and motor don't cause over-temperature shutdown, it should work.

    I also recommend to check if the relays cause any voltage spikes at the output. These spikes may cause problems driving the motor and may trigger over-current protection. Or worst, it may cause damage to the device if there are large voltage spikes. If you do observe voltage spikes due to the relays, I recommend adding  a few transient voltage suppression diodes.

  • 0
    TI__Guru 56650 points

    Oba，

    My concern：when the relay is switching with the motor coil current, the high di/dt could generate a high voltage on DRV8876 OUT2 pin or the relay terminal.

    To eliminate the high voltage spike, we may need to add extra circuit.

    If we really want bi-direction current control on two motors, we may need two motor drivers.

  • 0 in reply to Wang5577
    TI__Genius 15770 points

    Hello,

    They don't switch the relay during the motor current existing.
    Do you still see any problem?

    Regards,
    Oba

  • 0 in reply to Oba
    TI__Mastermind 37683 points

    Hi Oba,

    I'm a bit confused as for the need of the relays. Are the relays used for safety purposes like disconnecting the motor in the case of high currents or voltages?

    If the relays are closed before the H-bridge outputs are enabled, I think it is okay. There might be some spikes due to the added parasitic inductance of the relay. if the spikes are acceptable for your application, you might not have have to add extra circuitry to eliminate the spikes. I recommend evaluating with an evaluation board.

  • 0 in reply to Pablo Armet
    TI__Genius 15770 points

    Hello Armet,

    They don't use these 2 motors simultaneously and the host MCU doesn't enough GPIOs to connect 2 DRV8876.
    This is the reason that they put relays.

    They will switch the relays when the device in "Coast, OUT1/2 =Hi-Z" state.

    They may also switch when the device is in "Brake, OUT1/2=LOW) state. 
    Is it OK to switch relay in this state if the motor is absolutely stop?

    Regards,
    Oba

  • +1 in reply to Oba
    TI__Mastermind 37683 points

    Hello Oba,

    If the relay is switch when the motor is fully stopped and the winding current has decay all the way to 0-A, then there should be no problem. But if the relay is switched whiled there is still some current in the motor winding, the relay switching can cause high voltage spikes as Wang explained in a previous reply. The driver can be used in the configuration that the customer wants but extra protection circuitry will be needed to suppress any voltage spikes on the motor current path.