LM5001: What's the use of RC accross diode on EVM ?

Eric HEURTEL

Part Number: LM5001

On LM5001 Boost Evalboard, and also on LM5001 schem generated by Webench, there is a RC (6.8R+470pF) in parallel to rectifer diode. It's the first time I see this, and there is no explanation, nor in Datasheet, neither in the many Boost related Application Notes. What's the use of this ? Is it because of high-voltage outputs (48V), or because the switch is NPN ? How to calculate these components values ? What's the impact on efficiency ? What of conducted EMI, and output noise ?

Thank you in advance,

E. HEURTEL

over 8 years ago

0 Vincenzo Pizzolante over 8 years ago

TI__Mastermind 25486 points

hi Eric,

the RC network you mentioned is a snubber network, and is used to suppress RF noise generate by the ringing generated by the LC tank created by the parasitic of the diode + layout... you might need 2 actually, because another tank is around the FET (if external)...

it reduces a little bit efficiency but saves your life in EMI compliance tests :)

calculation comes from the test performed w/o the snubber and then fine-tuned to get the best tradeoff perfomance/EMI...

refer to slva255, slyt465 and this post for details

Vincenzo

0 Eric HEURTEL over 8 years ago in reply to Vincenzo Pizzolante

Prodigy 130 points

Thank you very much for this clear explanation !

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LM5001: What's the use of RC accross diode on EVM ?