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LM5116: Input capacitor selection...

Andrew Frazer
Expert 2305 points
Part Number: LM5116

I am wanting to design a 48V -> 5V converter, which will operate up to 20A, using the LM5116.     I use a lot of the 5116 for other devices, and reusing it is very helpful.

I've calculated that i need 100uF of input capacitance for this..         Previously i've used Ceramic Caps,   ( 10uF/100V ).. for one design i've put 2 in parallel to get 20uF.. 
I know i need to use something that has low ESR to stop ringing occurring in the circuit..      

Are there any recommended alternatives to using ceramics..  Could I use s low ESR electrolytic?       

Section 8.2.2.7 of the datasheet has a calculation for calculating the damping factor. .     I'm having trouble ( due to a lack of understanding ) of  calcluating Zs..  I dont' know what Lin is or how to calculate it..

Could anyone provide any insight?

  • 0
    TI__Mastermind 23845 points
    Actually the dampening is achieved by adding ESR into the input capacitor. If you have a long lead length to the input of your supply, you might want to add an aluminum electrolytic capacitor to dampen your input such that the voltage at the VIN pin is less than 100V.

    So yes, you can use an electrolytic capacitor in combination with a small ceramic for high frequency ripple at the input.

    Thanks
    -Arief