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DRV8818: PWM noise

NAOKI AOYAMA
Guru 11215 points
Part Number: DRV8818


Hello,

Our customer use the DRV8818.

There is the PWM noise on the VCC, Vref and STEP pin.

I attach the results of the customer's estimation.

DRV8818_PWM_noise.pdf

The configuration of the customer as follows.

1/2 STEP , 1.2A peak current

bypass capacitor: VMA 0.1uF VMB 0.1uF VCC:0.1uF and bulk capacitor as 330uF

Especially, the noise of STEP pin is over +/-1V. 

Does this noise cause to malfunction or damage the device?

Do you have any workaround?

Best Regards,

Naoki Aoyama

  • 0
    TI__Guru** 114905 points
    Hi Aoyama-san,

    The noise shown is typical in this type of system. We have not observed any issues with the device unless the noise spikes exceed the positive threshold of the STEP pin.

    If the noise exceeds ~0.3 x VCC on the STEP pin, it could be interpreted as a STEP pulse, causing the indexer to advance.
  • 0 in reply to Rick Duncan
    TI__Guru** 114905 points
    Hi Aoyama-san,

    Sorry, please let me correct the statement " We have not observed any issues with the device unless the noise spikes exceed the positive threshold of the STEP pin."

    I should have written: We have not observed any issues with the device unless the noise spikes exceed the maximum Vil threshold of the STEP pin.
  • 0 in reply to Rick Duncan
    Guru 11215 points
    Hi Rick-san,

    Thank you for your reply.
    The customer consider the level of the spike noise below GND.
    Is there any absolute maximum ratings about STEP pin with short duration spike noise?

    Do these spike noise occur depending on the measurement condition?

    Regards,
    Naoki Aoyama
  • 0 in reply to NAOKI AOYAMA
    TI__Guru** 114905 points

    Hi Aoyama-san,

    The absolute maximum rating is -0.5V with respect to device GND (pins 7 and 21).

    It is important that the measurements are taken with respect to device GND.

    Ideally a differential probe is best to perform this measurement. Another option is to measure the STEP pins and GND pins with respect to a ground and use the math function.

  • 0 in reply to Rick Duncan
    Guru 11215 points
    Hi Rick-san,

    Thank you for your reply.
    I will check the measurement condition of the customer.

    I want to ask one more question.
    The absolute maximum ratings of the VREF pin is 0V(GND) to VCC.
    In most case, it is -0.3V to VCC+0.3V.
    Is there any reason?

    Regards,
    Naoki Aoyama