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DRV8870EVK issue

Jesus Alonso
Prodigy 30 points
Other Parts Discussed in Thread: DRV8870

Hello.

On the first test of the DRV8870 Eval Board I noticed acoustic noise on the motor.

After measuring the 555 output, it is around 2.8KHz, but as stated on the DRV8870EVK manual, it would be aprox 25KHz: "...The “PWM” signal generated by the onboard circuitry EVM is approximately 25 kHz"

Please comment.

  • 0
    TI__Guru** 114905 points

    Hi Jasper,

    Our apologies. The capacitor (C2) is incorrectly sized for the 25kHz PWM frequency. This is being remedied in subsequent builds. If you would like a 25kHz frequency, change capacitor C2 from 10nF to 1nF.

    The User's Guide will be updated to reflect this.

    FYI -- in most cases, there is no need to PWM the input. The device is intended to be driven with a logic 1 on one input and a logic 0 on the opposite input. The PWM'ing is handled automatically by the device.

    Sorry for any inconvenience.

  • 0 in reply to Rick Duncan
    Prodigy 30 points
    Hello Rick.

    Thank you for your quick reply.
    It's OK to change C2. I will test it.
    Anyway, also a noise is produced W/O using PWM when adjusting Vref at its adecuate level.
    What can you recommend to smooth this noise?
  • 0 in reply to Jesus Alonso
    TI__Guru** 114905 points
    Hi Jasper,

    Can you provide more information on the noise w/o using PWM. Please provide a scope capture the output voltages when the noise is present.

    If correctly operating, the outputs should either static, or regulating current by between drive (one output high and the other low) and slow current decay (both outputs low) for 25us. If the time is longer than 25us, this indicates some other event.