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DRV8832: current limit questions

Betty Guo
Expert 7300 points
Part Number: DRV8832

Hi,

Customer use DRV8832 test the current limit, have below questions:

1. VCC=6V VSET=1V Isense=0.33ohm, load is motor, DRV8832 report fault when the load current reach to 480mA , the over current time continued longer than  275ms.

2. VCC=4.2V VSET=1V Isense=0.33ohm, load is motor,  DRV8832 not report fault even the load current higer to 530mA, continued time longer than 275ms.

3. VCC=6V VSET=1V Isense=0.33ohm, load is 0.66ohm resistor, DRV8832 report fault when the current reach to 550mA,

accroding the Ilimit equation, the limit current is about 630mA, why there is a gap with 600mA? Is this normal for DRV8832? during the whole experiment, no UVLO, OCP and OTP.

I find the range of Vlimit is from 160mV to  240mV, but for the same on device, the Vlimit should be the same right? 

Any other reasones may caused the different fault current limit value?

thanks.

  • 0
    TI__Guru 56650 points

    Betty,

    1. Does the customer test the limit current on an EVM or their own board?

    2. Is the 480mA a peak current or the load average current? What is the motor inductance? Do you have scope pictures to share?

  • 0 in reply to Wang5577
    TI__Expert 7300 points

    Hi Wang,

    customer test on their board. and the 480mA is the peak current.

    below is the waveform:

    1. test 1 waveform, blue is the fault_n and green is current.

    test 2 wavform:

    test3 waveform:

  • 0 in reply to Betty Guo
    TI__Guru 56650 points

    Betty,

    It is measurement issue. Please zoom in the current waveform with 20us/div. With 1s/div and 1k sample/sec resolution (1ms only one sample), we cannot read out the peak current. BTW, DRV8832 PWM frequency is 44.5kHz. The cycle time is much shorter than 1ms. Please make the sample time 50x or 100x shorter than the PWM cycle time to catch the peak current.

    Also, the waveform 1 and 2 show the average current, not peak current.