Author Topic: Mosfet RC snubber for a buck boost controller  (Read 673 times)

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Offline RainmanTopic starter

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Mosfet RC snubber for a buck boost controller
« on: February 26, 2020, 11:29:43 pm »
Hello guys,

I have a buck boost regulator LT8390 from Analog/Linear running at 12V/8A output with a great amonunt of switching oscillations on the output. I want to add an RC snubber circuit to dampen the oscillations and have looked at a demo circuit schematic showing how it could be done. I have also read some theory about the subject.

Here is a link to the demo board schematic: https://www.analog.com/media/en/technical-documentation/eval-board-schematic/710-DC2825A_REV02_PCA_SCHEMATIC.pdf

From the demo schematics it is suggested to have RC snubber across mosfets M1 and M3. I can agree on the M3 snubber for boost mode operation, but other litterature is suggesting to have the snubber for buck mode operation placed across M2 and not M1 as the schematic is showing.

Anyone out there who has designed a similar thing and knows which mosfets to place the snubber across? I don’t have any footprints for snubber components om my current PCB so trial/testing is not so easy at the moment.

Best regards,
Rainman
 

Online thm_w

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Re: Mosfet RC snubber for a buck boost controller
« Reply #1 on: February 28, 2020, 01:32:47 am »
What is the switching frequency, 150-650kHz fixed or spread spectrum?
What are the switching oscillations on the output, noise, ripple? It may be necessary for an output filter instead.
Are they excessive in boost mode, in buck mode, or both?

Trial and testing will be necessary, solder components to the PCB, you may have to be creative and scrape off solder mask, etc.

Putting the snubber across M2 or M1 should not make much difference. You can test it for yourself. The DC voltage across the snubber may differ though.
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