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DRV8702-Q1: Is the Equation1 in DRV8702-Q1 datasheet (SLVSDR9D) correct?

Part Number: DRV8702-Q1

 Hello guys,

 One of my customers is about to start designing of their new products using DRV8702-Q1. They had the following question when they were checking DRV8702-Q1 datasheet.

 Could you please answer the following question?

 Q. They calculated I(CHOP) with Equation1 on page 24 in DRV8702 datasheet. Then they used the parameters described at same section as the below.

      Vvref=3.3V, VIO=50mV, R(sense)= 50mohm, Av=19.8V/V.

      But they didn't get 3.28A as the answer described at same sectin.

      Their question is whether the Equation1 in DRV8702-Q1 datasheet (SLVSDR9D) is correct or not.

  Your reply would be much appreciated.

 Best regards,

 Kazuya Nakai.

 

  • Hi Nakai-san,

    The equation 1 is not correct, and requires some additional clarification.

    In the numerator (Vvref - Vio x Av), the term Vio x Av is the voltage measured at the output of the SO pin with no load. The equation should be adjusted to

    Vvref - (Vio x Av)
    Ichop = --------------------- where (Vio x Av)
    Av x R(sense)

    Please see section 7.3.5 and Figure 34 for details.

    Also, the following thread was found: e2e.ti.com/.../686370
  • Hi Rick,

    Thank you for your prompt reply.

    Could I ask you one additional question? Because I couldn't get 3.28A as the calculation result.

    Q. DRV8702-Q1 datasheet (SLVSDR9D) says on page 24 "For example, if a 50-mΩ sense resistor and a VREF value of 3.3 V are selected,
    the full-scale chopping current is 3.28 A. The AV is 19.8 V/V and VIO is assumed to be 50 mV in this example".
    In these sentences, I think the portion "VIO is assumed to be 50 mV" should be not correct and it should be "VIO*Av is assumed
    to be 50 mV".
    Is my thought correct?

    Thank you again and best regards,
    Kazuya Nakai.
  • Hi Nakai-san,

    You are correct. "VIO is assumed to be 50mV" should be "Vio x Av is assumed to be 50mV"
  •  Hi Rick,

     Thank you for your reply!

     Best regards,

     Kazuya Nakai.