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DRV8836EVM low current

K F
Prodigy 110 points
Other Parts Discussed in Thread: DRV8836EVM

I have a problem with the DRV8836EVM. When I connect a motor, the EVM supplies a max of 800mA. If I connect my motor directly to the 3V power supply, the motor draws the full 1.5A specified for my motor.

 

Interestingly if I combine the two halves of the HBridge together the motor still only pulls 800mA, with each half of the HBridge supplying a measured 400mA.

The voltage out on pins A1OUT A2OUT is 3V, so it seems to be a current limitation.

 

I'm running the EVM in "IN/IN" mode and I'm using the onboard toggle switches to control the motor.

 

Can someone please advise what could be causing this, and recommend some possible solutions.

 

Thanks in advance.

  • 0
    TI__Mastermind 21320 points

    Hi,

    What kind of motor are you driving (sounds like a DC motor)? Can you verify the voltage across the outputs/motor, not just the voltage to GND.

  • 0 in reply to Nicholas Oborny
    Prodigy 110 points

    yes it is a 3V DC motor. I verified the voltage across the output to the motor and that is the same as my input voltage, which is 3V.

     

    I just hooked up the EVM to a regulated power supply. I get the required current (1.5A) when I apply a minimum 4.5V to the EVM. Could the problem lie on the voltage regulator down on the EVM? 

     

    The documentation says 2V-7V can be applied to the EVM, but perhaps lower voltage prevents the proper current draw?

  • 0 in reply to K F
    TI__Mastermind 21320 points

    An H-Bridge will never supply the same amount as a direct connection to VM. This is due to the RDS(on) of the power FETs. You should be measuring a voltage less than the supply if you are measuring across the motor leads.

    The voltage regulator does not supply the power for the motor. What is the 3V power supply you are using?

  • 0 in reply to Nicholas Oborny
    Prodigy 110 points

    I've tried with a 3V Alkaline battery supply & also with a regulated supply connected directly to a wall outlet. Same result with both units...