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DRV8811: DRV8811 USMx Pull-up resistance value

Nariaki Ogasawara
Intellectual 1215 points
Part Number: DRV8811

Hi team,

 The customer's board was USMx pin was pull-up at 10K ohm, but the system was malfunction. The issue was improved when the resistance was changed to 1K ohm

My customer is asking below.

1. The measurement waveform at USMx seemed noisy during motor working although VCC did not seem noise.The noise reduced when resistance value changed from 10K ohm to 1K ohm.

    Is this noise comping from DRV8811 or not?

2.  What is recommended resistance value for pull-up? 

Regards,

Ogasawara

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

    1. The measurement waveform at USMx seemed noisy during motor working although VCC did not seem noise.The noise reduced when resistance value changed from 10K ohm to 1K ohm.

    Is this noise comping from DRV8811 or not?

    The system is generally noisy as the DRV8811 outputs switch on and off. Higher currents and temperatures increase the noise. Signal routing of the USM pins can also affect the noise.

    We have seen where glitches on pins can cause the inputs to misbehave. If the noise causes the USM pins to droop below .7 x VCC, the signal can be incorrectly interpreted.

    2. What is recommended resistance value for pull-up?

    The general recommendation for external resistors on input pins is “lower is better” to increase the noise margin. A 1kOhm is a good starting point because it has little effect on the system current. It is important to keep the noise below 0.3 x VCC when setting a logic low and above the 0.7 x VCC when setting a logic high.