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Ringing on output of DRV8432

Other Parts Discussed in Thread: DRV8432EVM

Hello, I am using the DRV8432 in my design, and I am getting a lot of ringing on the output at the solenoids, and motors that I am controlling. I have followed the recommended design that was given by TI, and I am curious to see if you have experienced this before. On the eval board there are inductors on the outputs of the driver. Can you tell me what they are used for? It seems that when I remove those inductors I still get some ringing, but it is much less. Below is a schematic of the circuit and the output of the driver at the load.

Thanks,


Rob

  • Hi Rob,

    The inductors on the EVM are used to allow paralleling the outputs. If you are not running the outputs in mode 3 (parallel), they are not required.

    I have seen ringing before, but not at this magnitude. I did not see a bulk capacitor on your schematic. Did I miss it? If there is no bulk, please place a large capacitor across PVDD and GND. A good start would be 2uF/W.

    Let us know if this helps.

  • Rob,

    Snnuber circuit i.e. combination of series capacitor (typically 0.1uF) and resistors (10 to 10ohm) across each outputs and GND should also help in reduce the ringing.

    Best Regards

    Milan -Motor Application Team

  • Thank you Rick and Milan, after removing the inductor a lot of the ringing was removed. The snubber is a good idea as well. I will add it to the output. Rick, I do have a bulk cap on PVDD that is not shown on this schematic. It is located at the power connector similar to the 1000uf C1 that is on the eval board. We will try a few more things here, but it looks like removing the inductors from the board will make the biggest improvement, and the rest we should be able to filter out with the snubber and diode array.

    Rob

  • Hi Rick and Milan, I went back to have a look at the waveform on the DRV8432EVM Board, and I see the same noise at the same frequency of about 111.111MHz. With my PVDD set to 24V this is giving me a ripple with an amplitude of 7.4V. Below is a screen capture of the ripple I am seeing on the rising pulse. The same ripple is present on the falling edge of the output PWM from the DRV8432. Any thoughts on getting rid of this?

    Rob

  • Hi Rob,

    Last time, you mentioned that you planned to add a snubber. Have you done so, and what values did you use?

    While not exactly the same because the FETs are external and the application is a buck converter, the application note on the NexFET provides insight on the problem and how to correct it. The link to the app note is:

    http://www.ti.com/general/docs/lit/getliterature.tsp?baseLiteratureNumber=slpa010

    For reference, I found this by searching the TI site for "snubber application note".

    The app note requests one piece of information that is not provided in the DRV8432 datasheet. I will get back with you once I have the estimated Cp.

  • Hi Rick, I have tried several different snubbers and the one that worked the best had R = 15ohms, and C = 10uF. The problem with this is the power dissipated through the resister is huge! (Almost 4W) That configuration reduced the amplitude of the ringing, but not enough. I will take a look at the app note now.

    Rob

  • Hi Rick, were you able to find the estimate of Cp yet? Thanks,

    Rob

  • Hi Rob,

    Sorry for the delay. I don't have it yet, but I am trying an alternate path. Will shoot you an update either way by the end of the day.

  • Hi Rob,

    I have not heard back from my contacts. It may take a couple of days. I will post as soon as available.

    Until I get the typical value for the DRV8432, I searched for a comparable FET available through distributors. Finding a 75V Vds max, 10A, 130mOhm FET, the Coss was 30pF.

    You can use this as a starting point. Good luck, and again sorry for the delay.

  • Hi Rob,

    I got the information. The typical value  for the DRV8432 is 250pF.

     

     

  • Hi,

    I am using DRV8432 in Parallel full bridge mode. I am getting a lot of ringing on the output at the inductors. Please share the snubber circuit which you have designed for DRV8432 and the location to place the circuit.
    I hope it may help me to get rid of the ringing.
  • I found this post that may be of benefit: e2e.ti.com/.../403063
  • Hello Rick,

    We're having the same ringing issue in our design.  We added the inductors at the outputs as short circuit protection, but due to the large ringing our motor current measurements show large spikes.  When we tested our boards after removing the inductors, the ringing peak to peak voltage reduced from 57V to 36V.  Per your response to Robert, the inductors are not required if the outputs not running in parallel mode.  We're considering to remove the inductors from our boards since we're running two motors in dual full bridge mode.  Could you please let me know if it would be OK to do that without any other consequences?

    Thanks,

  • Hi Rainbow,

    The inductors are not required, but are recommended if you desire to protect the outputs against possible short circuits to high current signals (PVDD, GND).

    Please note section 7.3.2.2 of the datasheet. This section contains a recommendation to limit the current by adding a ferrite bead or inductor to protect the output pin against a short to power or gnd.
  • Hi Rick,

    Thanks for your prompt response! I have another question related to the ringing output. The datasheet shows that a snubber is added at the PVDD node on page 17. In our design we didn't add the snubber because the datasheet states that no external snubber of schottky diode is required on page 1. Don't we need the snubber in order to reduce the ringing caused by the inductors at the output?
  • Hi Rick,

    I would appreciate it if you could respond to my question quickly because we need to complete our design very soon.

    Thanks,
  • Hi Rainbow,

    The snubber is not required in all cases. Your application may be better suited for a snubber.

    If in doubt placing the footprints for the snubber is a good idea. If you do not need it, the component cost can be reduced.
  • Thank you for all your help, Rick!

  • Hi Rick,

    I added a snubber consisting of a 10 OHM resistor and a 0.1 uF capacitor between PVDD and GND. But, I didn't see any ripple reduction from the DRV8432 output voltage. But, adding the snubber in paralled across a motor which is run by the output voltages reduced the output ripple voltage from 3V to 1V.

    In the datasheet the snubber is added between PVDD and GND. Is the snubber used to maintain a good signal on PVDD instead of reducing the output voltage ripples? Do I need to add the snubber across the motor in order to reduce the DRV8432 output ripple voltages?

    Thanks,