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DRV8899-Q1: Slew rate setting

Yusuke Okamoto
Intellectual 1600 points
Part Number: DRV8899-Q1

Tool/software:

Hi Experts,

Could you tell me definition of SLEW_RATE resister setting?

According to datasheet, the SLEW_RATE value is tied to Blanking time in Table 7-8 however  SLEW_RATE is stated by V/us in Resister map (Table 7-21).

Could you tell me which value should be referred, Table 7-8 or Table 7-21?

Best Regards,

Yusuke

  • +1
    TI__Expert 5120 points

    Hi Yusuke-san, 

    Thank you for your question. The tblank is the time that the current sense comparator is ignored before checking the current. The blanking time also sets the minimum drive time of the PWM. The slew rate also controls the rise the fall time of the output voltage. or in other words the slew rate determines how quickly the driver changes the voltage at the outputs. 

    The SLEW_RATE bit control both the slew rate and tblank time under the fast decay mode. If you set the SLEW_RATE bit equal 00b the slew rate will be 10V/us with 5.6 us tblank time under the fast decay mode

    Please let me know if you have any more questions. 

    Best regards, 

    Mojtaba.

  • 0 in reply to Mojtaba Afshar
    TI__Intellectual 1600 points

    Hi Mojtaba,

    Thank you for your answer.

    Just to be sure, the slew rate represents the slew rate of the gate voltage of the FET drive, right? 

    Best Regards,

    Yusuke

  • +1 in reply to Yusuke Okamoto
    TI__Expert 5120 points

    Hi Yusuke-san, 

    Thank you for your question. 

    Yusuke Okamoto said:
    Just to be sure, the slew rate represents the slew rate of the gate voltage of the FET drive, right? 

    The Slew rate shows the output voltage changes per us. It shows how quickly the output voltage transition during switching. The DRV8889 internally control the gate driver in a way to result in a desire rise and fall time. 

    Please let me know if you have any more questions. 

    Best regards, 

    Mojtaba

  • 0 in reply to Mojtaba Afshar
    TI__Intellectual 1600 points

    Hi Mojtaba,

    Thank you for your relpay.

    It is my understanding that the blanking time is set to be rewritten in the same register when the slew rate is increased, because it is dangerous for the operation if it is not set short. Is this understanding correct?

    Best Regards,

    Yusuke

  • +1 in reply to Yusuke Okamoto
    TI__Expert 5120 points

    Hi Yusuke-san, 

    That is correct. For higher slew rate, lower blanking time is set. 

    Best regards

    Mojtaba

  • 0 in reply to Mojtaba Afshar
    TI__Intellectual 1600 points

    Hi Mojtaba,

    Thank you for your answer.

    Mojtaba Afshar said:
    The SLEW_RATE bit control both the slew rate and tblank time under the fast decay mode. If you set the SLEW_RATE bit equal 00b the slew rate will be 10V/us with 5.6 us tblank time under the fast decay mode

    Is Blanking time 500ns fixed value when we use under slow decay mode?

    Best Regards,

    Yusuke 

  • +1 in reply to Yusuke Okamoto
    TI__Expert 5120 points

    Hi Yusuke-san, 

    Yes blanking time is fixed and about 500ns under slow decay mode. 

    Best regards, 

    Mojtaba

  • +1 in reply to Mojtaba Afshar
    TI__Intellectual 1600 points

    Hi Mojtaba,

    Thank you for your support!

    If blanking time is fixed at 500ns, am I right in thinking that the slew rate cannot be changed in slow decay mode? Or does it mean that the blanking time remains the same, but the slew rate can be changed?

    Best Regards,

    Yusuke

  • +1 in reply to Yusuke Okamoto
    TI__Expert 5120 points

    Hi Yusuke-san, 

    Thank you for your question, 

    Yusuke Okamoto said:
    If blanking time is fixed at 500ns, am I right in thinking that the slew rate cannot be changed in slow decay mode? Or does it mean that the blanking time remains the same, but the slew rate can be changed?

    The output slew rate can be modified in all decay modes. However, the blanking time is fixed 500 ns for slow decay mode and can be set for fast decay mode at different values.

    Best regards, 
    Mojtaba