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Observation on DRV8701EVM Performance with high PWM frequency and low duty cycle

Wei Meng Ooi
Prodigy 70 points
Other Parts Discussed in Thread: DRV8701, DRV8701EVM

HI,

I have few question regarding DRV8701:

1) What is the minimum allowable operating PWM pulse width for DRV8701?

2) I am using 64kHz PWM frequency in my application. With DRV8701EVM (Eval-board), I am seeing in consistent output  (even missing pulse ) if the PWM pulse width is shorter than 8us. Please refer to attached file ( WAVEFORM-1.xlsx and Missing Pulse.xlsx) for detail.

WAVEFORM-1.xlsxMissing pulse.xlsx

May I know the reason ?

3) I am also seeing inconsistent output rise time with short PWM pulse width. Please refer to attached file:Inconsistent Output Rise time.xlsx

May I know the reason?

  • 0
    TI__Mastermind 26065 points
    Hi Wei,

    We will look into this and get back later.

    Best regards,
  • 0 in reply to Wilson Zuo
    Prodigy 70 points

    Hi Wilson,

    I have not hear from you on my question.

    Here is the update on my investigation:

    Please ignore question 2 and 3, once the load is connected across the H-bridge, the problems with inconsistent rise time goes away.

    There are few more question on the part:

    1) Under 6.5 Electrical Characteristics, the Output dead time is specified as 380ns with remark (Observed tdead depends on IDRIVE setting), what is the IDRIVE setting for  380ns?  Is this 380ns an observed dead time with particular IDRIVE setting? What is the guaranteed dead time without considering the IDRIVE setting ?  

    2) Attached is the waveform measured comparing GL1, GH1 and output. It takes about 350ns (dead time) for GL1 to starts to rise after GH1 gone low completely.

    My assumption is I should see around 150ns ( as mentioned in page 21) in this case. This is measured with DRV8701 eval board.

    .

    3) When pulse width is reduce, I observed the fall time increase with same IDRIVE setting. Attached are the waveform with max IDRIVE setting:

    Trace C2 : EN

    Trace C3 : Output (SH1)

    Trace C4 :GH1

  • 0 in reply to Wei Meng Ooi
    TI__Mastermind 26065 points
    Hi Wei Meng

    Sorry for the late response. We still need some more time to answer you question. Also there is a good note for the pre-driver parameters. www.ti.com/.../slva714.pdf . If you haven't read about it, you can do it before we give the answer to your questions.

    Best regards,