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DRV8886ATEVM: Current setting of DRV8886ATEVM

NOBUO FUJIHARA
Expert 8265 points
Part Number: DRV8886ATEVM
Other Parts Discussed in Thread: DRV8886EVM, DRV8885EVM, DRV8886AT, DRV8886

Hi Team,

My customer asked below, regarding to current setting of DRV8886ATEVM.

When customer configured IFULL SCALE as 1A, but actual measured current is 1.5A, with DRV8886ATEVM.

But with same current setting for  DRV8886EVM / DRV8885EVM , measured current flows was 1A as expected.

Attached is software version info, and dumped setting file.

Could you check what causes this mismatch?

Best regards,

settings.zip

  • 0
    TI__Guru 56650 points

    Fujihara-san,

    DRV8886AT and DRV8886 should have the same current limit.

    1. Please help me measure the RREF pin voltage between good one and bad one.

    2. Can they measure the winding current between good one and bad one? I am worry about some abnormal winding current waveform make the difference.

  • 0 in reply to Wang5577
    TI__Expert 8265 points

    Hi Wang-san,

    Thanks for your prompt reply.

    I will confirm with customer about RREF and if current waveform is available.

    In parallel, could you check if you can reproduce same phenomenon with DRV8886ATEVM + attached setting file?

    Best regards,

  • 0 in reply to NOBUO FUJIHARA
    TI__Expert 8265 points

    Hi Wang-san,

    1. Please help me measure the RREF pin voltage between good one and bad one.

    TIJ) Voltage on RREF  = 0.45V.

    2. Can they measure the winding current between good one and bad one? I am worry about some abnormal winding current waveform make the difference.

    TIJ) Please refer attached waveform.

    Beset regards,

    Motor Current.pdf

  • 0 in reply to NOBUO FUJIHARA
    TI__Guru 56650 points

    Fujihara-san:

    If they don't change the RREF pin resistor, the series RREF resistor should be 15kohm.

    If the MCU side RREF resistor voltage is 0.45V, the current should be 1.27A according to the datasheet equation 2

    Three things I can think of:

    1. RREF series resistor value is shifted to a lower value. Please check that resistor value.

    2. MCU try to set 0.6V to get 1A. But, the measurement is 0.45V. The MCU got damage. Please compare it with the good board RREF resistor voltage.

    3. The early released engineer board may not have 15kohm RREF resistor. (In this case, please take a picture of the board). 

  • 0 in reply to Wang5577
    TI__Expert 8265 points

    Hi Wang-san,

    Thanks for your answer.

    For 1 and 3,  I will ask customer to check RREF resistor value.

    Regarding to 2, customer has already confirmed no issue on DRV8886EVM and DRV8885EVM as I mentioned before.

    Could you double check if it's operating correctly on your environment?

    Best regards,

  • 0 in reply to NOBUO FUJIHARA
    TI__Guru 56650 points

    Fujihara-san:

    After IT group fixed the installation issue, I can run DRV8886AT today. On my EVM, the peak current is 1A with the follow GUI setup. Peak current keeps same with different micro-step setting. Also, the RREF resistor R1 on MCU side voltage is 0.617V. If RREF_R test point on J4-10 is 0.54V, either 15kohm R1 is less than 15kohm or MCU cannot drive the R1 to 0.617V. 

  • 0 in reply to Wang5577
    TI__Expert 8265 points

    Wang-san,

    Thanks a lot for your prompt support.

    It seems R1 has changed at customer's board, I will discuss with customer to replace it to 15kohm.

    Best regards