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DRV8718-Q1: About PWM control and CSA gain

Yuya Shoji
Expert 5520 points
Part Number: DRV8718-Q1
Other Parts Discussed in Thread: DRV8714-Q1
  1. DRV8718 can drive 4 motors respectively with PWM control, right?
  2. Could you tell me CSA gain accuracy and its slew rate of DRV8718?
  • 0
    TI__Mastermind 37683 points

    Hi Yuya,

    Yuya Shoji said:
    DRV8718 can drive 4 motors respectively with PWM control, right?

    Yes. The control mode should be set to half-bridge control. However, the motors can only be controlled unidirectionally. 

    Yuya Shoji said:
    Could you tell me CSA gain accuracy and its slew rate of DRV8718?

    The CSA accuracy is given in the datasheet electrical characteristics table (shown below). 

    The switch node slew rate is programmable via the IDRIVEP_x and IDRIVEN_x register fields. The slew rate can be calculated by equation t_slew = Q_GD/IDRIVE (where Q_GD is the gate drive charge and IDRIVE is the programmed IDRIVE value.

    Regards,

    pablo Armet

  • 0 in reply to Pablo Armet
    TI__Expert 5520 points

    Thank you for your reply!

    Pablo Armet said:
    However, the motors can only be controlled unidirectionally.

    What about below case:

    HB1_CTRL = PWM, HB1_PWM=IN1, HB2_CTRL = L, HB2_PWM=n/a

    -> HB1_CTRL = L, HB1_PWM=n/a, HB2_CTRL = PWM, HB2_PWM=IN1

    This H-bridge can work as bidirectionally, right?

    So, I'm thinking that DRV8718-Q1 can drive 4 motors bidirectionally referencing 4 different PWM signal applied to IN1-IN4 pins.

    Pablo Armet said:
    The switch node slew rate is programmable via the IDRIVEP_x and IDRIVEN_x register fields.

    Do you have CSA's slew rate data?

    Regards,

  • 0 in reply to Yuya Shoji
    TI__Mastermind 37683 points

    Hi Yuya,

    Yuya Shoji said:
    This H-bridge can work as bidirectionally, right?

    Correct. There are 8 half-bridges and 2 are required for bi-directional control. I confused this device with the DRV8714-Q1 which only has 4 half-bridges. Apologies for that misunderstanding.

    Yuya Shoji said:
    Do you have CSA's slew rate data?

    Can you clarify what you mean by CSA slew rate? 

    Regards,

    Pablo Armet

  • 0 in reply to Pablo Armet
    TI__Expert 5520 points
    Pablo Armet said:
    Correct. There are 8 half-bridges and 2 are required for bi-directional control. I confused this device with the DRV8714-Q1 which only has 4 half-bridges. Apologies for that misunderstanding.

    No worry. Thanks a lot!

    Pablo Armet said:
    Can you clarify what you mean by CSA slew rate? 

    This device contains current sense amplifier, so I'd like to know this amp's slew rate (V/us).

  • 0 in reply to Yuya Shoji
    TI__Mastermind 37683 points

    Yuya,

    I will need 24 hours to find the information you are asking for.

    Regards,

    Pablo Armet

  • +1 in reply to Pablo Armet
    TI__Mastermind 37683 points

    Hi yuya,

    I have provided the information you request over email. Below is my response:

    Based on the DRV8718-Q1 datasheet EC table, the slew rate is 2.5 V/µs when C_SO = 60pF and the standard test parameters listed in the EC table.

    The OP2376 slew rate spec is also given in its datasheet and it is 2V/µs with G=1, C_L=100pF, and Vs=5.5V.

    Let me know if this is enough information to provide the customer

    Regards,

    Pablo Armet