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DRV8872: motor does affect the speed of other

May
Genius 9880 points
Part Number: DRV8872
Other Parts Discussed in Thread: DRV8871

Hi,

Customer have encounter an issue regarding their design, please see details below.

I am working on a circuit in which I am using three DC motors whose rated current is 24V. I am using three DRV8872 motor drivers to control each of them but I have noticed very abnormal behavior of motors. If I put more torque on one of the other motor speed decreases so all motor connected with same power rail in the PCB which is VM. I want to know why it is happening? How I can avoid that load on one motor does not affect the speed of other. The value of Rsense resistor is 150 ohm.



It is happening with the earlier driver also which was DRV8871

Thank you in advance.

Regards,
Maynard

  • 0
    TI__Guru 54645 points

    Maynard,

    And VM is constant...does not change when loading the one motor?  It seems that VM would have to change to affect the other motor driver behavior.

    Regards,

    Ryan

  • 0 in reply to Ryan Kehr
    TI__Genius 9880 points

    Hi Ryan,

    Just received response from customer, please see details below.

    VM voltage change when loading the motor if VM voltage is 25 V with no load on motor then it drop to 19 V with load. I am directly operating motors using battery input there is no regulator circuit between battery input and VM

    Regards,
    Maynard

  • 0 in reply to May
    TI__Guru 54645 points

    Maynard,

    It makes sense then as the VM change would impact the other drivers.  There must be a high series resistance in the battery that causes that drop.  They can calculate it if they measure the current in the load.

    Also, Rsense should be very small like 0.2 ohms or similar.  150 ohms is way too high.  There is an equation in the datasheet.

    Regards,

    Ryan

  • 0
    Prodigy 41 points

    It looks like that the current of power supply is limited, if so I suggest that customer use a bigger power supply. Otherwise there should be a big resistance between Vbat and VM that caused a big voltage drop during this condition.

  • 0 in reply to Hongda Wu
    TI__Guru 54645 points

    OK, I will close this for now.  Thank you for the update.