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DRV8802 Control output current by VREF

na na78
Guru 16770 points
Other Parts Discussed in Thread: DRV8802-Q1, DRV8802EVM, DRV8802, DRV8412

Hi

We want to regulate winding current with DRV8802-Q1.

We refered SLVA416 application report and tried to do it with DRV8802EVM.

As an evaluation, the VREF input for DRV8802EVM is a sine wave from FG.


Other pin configuratin is following.

Enable A : Hi
Phase A : Hi
AI0 : Lo
AI1 : Lo
nRESET : Hi
nSLEEP : Hi
Decay : Lo

The output load is 20ohm and 0.44mH, a speaker.

(Rather than the speaker, we are going to use a VCM in actual system.)

As a result, we got the following output.

You can see the ripple on the output current.

Do you have any idea for eliminating it or reduce?

regards

  • 0
    TI__Guru** 114905 points
    Hi,

    What is your decay setting? If fast decay, please try slow decay. This may help some.

    If you need more current control, there may be better products available. Can you describe your requirements in more detail?
  • 0 in reply to Rick Duncan
    Guru 16770 points

    Hi Rick

    Thank you for your reply.

    We have already tried slow decay. The pin configuration is as below.

    Enable A : Hi
    Phase A : Hi
    AI0 : Lo
    AI1 : Lo
    nRESET : Hi
    nSLEEP : Hi
    Decay : Lo

    We expected smoother current regulation.

    So as our request, we want to know whether there is a way to reduce the ripple on output current using DRV8802Q1.

    Basically, is it possible to apply the SLVA416 application report to DRV8802?

    Or is the result we obtained is due to the capability of the DRV8802?

    regards

  • 0 in reply to na na78
    TI__Guru** 114905 points

    Hi,

    I don't think the DRV8802 will work in your application.

    There are a couple of items to consider.
    1) the accuracy of the comparator varies depending on the VREF input and can vary by up to 10%
    2) the PWM chopping can affect the current regulation. Once started, it may take up to 20us to start the next drive cycle.

    You probably need a different device, like an audio amplifier or the DRV8412. These devices can turn on and off very quickly. Additional circuitry is required to monitor the current.

  • 0 in reply to Rick Duncan
    Guru 16770 points
    Hi Rick

    Thank you for your advice.

    Actually, we are looking for the IC satisfying following, in the automotive rating.

    Supply: +/-15V to +/-20V
    Input : Analog wave (1.8Vpp, 2KHz) or PWM
    Output Current : Over 1A

    We can't find adequate one in the Op-amp lineup.
    So we referred SLVA416 application report and evaluated DRV8802Q1 which can control output current by Vref input, but it doesn't seem to work well.

    As you mentioned, we will need the device which can turn on and off more quickly.
    What kind of solution is suitable for this application?
    Do you have any idea?

    Best regards
  • 0 in reply to na na78
    TI__Guru** 114905 points
    Hi,

    Can you provide more details about the application?
    Will the current always be a 2kHz sine wave?
    How many points will there be on the sine wave input? (how fast is the sine wave input switching?)
    What is the desired accuracy of the current regulation?
    Any details you can share may help point us to a device.
  • 0 in reply to Rick Duncan
    Guru 16770 points
    Hi Rick

    Thank you for your reply.

    The maximum frequency is 2kHz.

    It is difficult to offer the information about the accuracy of the current regulation because we don't have the information how much accuracy is good.

    We will try to get the data continuously, and we are considering using discrete IC (Op-amp, FET) also.

    Maybe it will take a time, so we want to close this thread once.

    Thank you for your help.

    best regards