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Drv8412 Digital reference signal

Alvaro Martinez
Prodigy 110 points
Other Parts Discussed in Thread: DRV8412

Dear all,

We are using a power stage based on DRV8412. We are having some noise problems. We are analizing where is it coming from, maybe this board, but it could be from other point of our setup.

Reviewing the information of the DRV8412, we have some questions regarding the Ground signals. Which is the ground reference of the input TTL signals (PWM, reset, etc.? I guess it is what it is called AGND as it is the reference coming out from Vreg, but now I am not sure. 

Thank you in advance,

Alvaro

  • 0
    Prodigy 110 points
    Regarding this issue, it is suggested to install a R=1ohm to connect AGND and GND. As we are having high frequency problems, will it work to install a coil insted?
  • 0 in reply to Alvaro Martinez
    TI__Guru** 114905 points
    Hi Alvaro,

    AGND is the ground reference for the input TTL signals.

    It is recommended to use a resistor between AGND and GND. Use of an inductor could prevent current flow.
  • 0 in reply to Rick Duncan
    Prodigy 110 points
    Thank you Rick,

    It is a bit confussing because it could mean "Analog GND" and I undestand this is a "Digital GND".

    Regarding the second question, our idea would be to isolate the motor noise in the GND plane. I do not know if we will be able to do it with the coil (avoiding high frequency current flow). Maybe I have some concepts wrong... Do you think it might work?

    Thank you again,
    Alvaro
  • 0 in reply to Alvaro Martinez
    TI__Guru** 114905 points

    Hi Alvaro,

    It is confusing, but AGND carries current from critical references and logic circuits supplied by VDD.  These include VREF, OC_ADJ, input circuits, Mode pins, etc.

    GND carries current from higher power switching circuits supplied by VDD and GVDD.  These include drivers to the output FETs and the logic that feeds them.

    I suggest you take a look at the DRV8412EVM ( LINK ) There you will find the user guide, schematics, and gerber files showing how the DRV8412EVM was laid out.

    The intent is to place circuits so power ground currents do not flow toward the quiet side, but towards the power supply.

  • 0 in reply to Rick Duncan
    Prodigy 110 points
    Thank you Rick,

    I have seen that EVM and we are following it in our design. We will investigate if the noise comes from other parts of the system.

    Regards,
    Alvaro
  • 0 in reply to Rick Duncan
    Prodigy 30 points

    AS suggested in Layout Guideline, 2 Oz copper should be used for top & bottom layer.

    i have a doubt, is it for two layer board only. what, if i am using four layer board.

    please suggest.

    Thanks  & Regards

    Meet Payak

  • 0 in reply to meet payak
    TI__Guru** 114905 points
    Hi Meet,

    Adding two more layers will probably increase the size of the thermal plane. I would suggest use 2 Oz is preferred, but a minimum of 1 Oz copper should suffice. This really depends on your layout, component placement, and any additional heat sources added to the pcb.
  • 0 in reply to Rick Duncan
    Prodigy 30 points

    Hello Rick

    Thanks for your reply.  i am planing a four layer board, where i will plan all four layers with 1 Oz.

    i would like to hear comment for it. Because clad with 2 Oz is not as common as 1 Oz or 0.5 Oz.

    Regards

    Meet Payak

  • 0 in reply to meet payak
    TI__Guru** 114905 points
    Hi Meet,

    As mentioned, many factors can contribute to thermal performance. It is difficult to say if 1 oz will work without knowing the peak and average power used, size of your board, other heat sources, and the environment.

    There is much information regarding thermal performance available at www.ti.com/thermal