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

Eric HEURTEL
Prodigy 130 points
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

  • 0
    TI__Mastermind 24491 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

    KR

    Vincenzo

  • 0 in reply to Vincenzo Pizzolante
    Prodigy 130 points

    Thank you very much for this clear explanation !