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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.
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.
Rick DuncanMotor Applications Team
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In reply to Rick Duncan:
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.
Milan -Motor Application Team
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In reply to Milan Rajne:
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.
In reply to Rob Greenewald:
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?
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:
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.
Hi Rick, were you able to find the estimate of Cp yet? Thanks,
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.
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.
I got the information. The typical value for the DRV8432 is 250pF.
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