LM73605: EMI or SW noise inhibition solution

Vincent Li00

Intellectual 2035 points

Part Number: LM73605

Hi Guys

Our customer use LM73605 to realize 5A DCDC. About the SW ring inhibition, they think add a RC between VIN and SW pin. Just as below. Could you help me understand how to achieve SW ring inhibition? Any calculation documents? I think we should add this RC between Cboot and SW or RC snubber between SW and GND. right?

If their solution can inhibit the EMI. how to choose the RC value?

Thanks

-Pengfei

over 3 years ago

0 Orlando Murray over 3 years ago

TI__Mastermind 22299 points

Vincent,

See following blog and app note,

https://e2e.ti.com/blogs_/b/powerhouse/archive/2016/05/05/calculate-an-r-c-snubber-in-seven-steps

https://www.ti.com/lit/an/slyt465/slyt465.pdf

Hope this helps,

-Orlando

0 Vincent Li00 over 3 years ago in reply to Orlando Murray

TI__Intellectual 2035 points

Hi Orlando

Very useful paper. But these only focus on boot resistor, a high-side gate resistor, or a snubber. It doesn't explain my question. Could you help compare which one is more effictive by placing snubber across FET or across rectifier diode? or they are same impact for EMI?

Thanks

-Pengfei

0 Orlando Murray over 3 years ago in reply to Vincent Li00

TI__Mastermind 22299 points

Pengfei,

The snubber should be place across the lowside diode/MOSFET from SW to GND.

Never place anything extra in the boot-SW loop.

We never place the snubber across the high from VIN-SW. I think it could be bad as it AC-couples VIN and SW node.

-Orlando

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LM73605: EMI or SW noise inhibition solution