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DRV8872: PWM using under voltage protection

Justin Hinson1
Prodigy 20 points
Part Number: DRV8872

I have a product that is using a boost converter to deliver the power to the chip. The boost converter goes below the UVLO threshold during a stall condition. Once the UVLO is hit, the boost converter starts to recover passes above the upper threshold of the UVLO. The DRV8872 then passes current to motor again.

My question is, are there any adverse effects on the DRV8872 that I should be aware of when operating in this mode? 

If any other information is needed, please let me know. 

  • 0
    TI__Guru** 114905 points

    Hi Justin,

    There are no adverse effects to the device.

    The concern is that all systems will act the same way when boost converter, capacitor, DRV8872, load, and temperature variations are considered.

    Will every system recover as you described, or will some get stuck in a loop between DRV8872 outputs enabled -> stall -> UVLO -> boost recovery -> stall -> UVLO -> etc.

    Please consider this scenario carefully. If you have not done so, please consider setting the maximum stall current using a resistor on the ISEN pin, or adjusting the input PWM frequency to limit the current during startup/stall.

  • 0 in reply to Rick Duncan
    Prodigy 20 points

    Rick,

    Thanks for the response, the product uses a power supply with a battery backup. When on the power supply, the motor pulls 9V 1A from the boost converter in a stalled condition. We would like to hold this for a maximum of 30 to try and brake the motor free. there are no issues in this situation.

    When the device is operating on battery, the boost converter drops and hits the UVLO and then it recovers. The result of this is a continuous loop for approx 30sec.

    Exactly what you were saying **** Will every system recover as you described, or will some get stuck in a loop between DRV8872 outputs enabled -> stall -> UVLO -> boost recovery -> stall -> UVLO -> etc.*****

    See current/Voltage waveform below. I am happy with these results, because it is auto adjusting the power going to the motor due to the battery voltage. Just wondering if there is any issue using it this way.

        

  • 0 in reply to Justin Hinson1
    TI__Guru** 114905 points

    Hi Justin,

    No issues. This is very similar to the overcurrent use case which disables the outputs for 3ms.

    Have you considered setting the boost to the same voltage as the power supply and limiting the current to 0.8A to 0.95A using ~0.39Ohm resistor? With the current regulation feature (slow decay) of the DRV8872, the outputs may provide similar current using the battery boost as the power supply without the boost voltage drooping.