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DRV8838EVM: High Ripple On the Motor Input Voltage

Victor Lerner
Prodigy 10 points
Part Number: DRV8838EVM
Other Parts Discussed in Thread: DRV8838,

I am trying to drive a peltier cooler with this eval board. I can drive the cooler but I am seeing close to 0.5 v pp ripple on Vm voltage at 3.3 v applied at VM.  I tried to ad 400 uF capacitor on Vm  rail but no avail. I cannot even drive the 2 ohm power resistor without the o.5 v ripple  on VM. This ripple is way to high.

  • 0
    TI__Guru 56650 points

    Victor,

    DRV8838 is a motor driver device. The load should be a high inductive load which can have a small ripple current and give small ripple at VM. But, if the load is resistor, the load current jumps from zero to full scale setting during the each PWM cycle. DRV8838 is just a switch (which doesn't have a filter function by itself.

    Do you use DRV8838 to drive a motor? If yes, you can put the motor on the DRV8838EVM output and monitor the VM ripple.

    If you want to drive a resistor load, the ripple voltage is Vripple = Iload*ton /Cvm. You can try to set a high PWM frequency from input signal to reduce high side FET turn-on time Ton. Or you have to increase the VM capacitance.