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WEBENCH® Tools/LM5141-Q1: Maximum values Inductor and Sense Resistor

Carlos Rodriguez1
Intellectual 345 points
Part Number: LM5141-Q1
Other Parts Discussed in Thread: LM5141

Tool/software: WEBENCH® Design Tools

Hi all, 

I am currently designing power supply based on LM5141/Q1, please find requirements below:

Input: 6-36V

Output 3.3V 9A

Operating Temperature 85°

Webench is giving to me, Inductor value of 3.3uH working at Fsw: 403kHz, but I would like to oversize the inductor, to have less current ripple, since my undertanding, is not a problem to use a 4.7uH, I have just checked with the datasheet, and I must use Inductor value higher than 3.03uH. But in this case, the Webench is recomending to me value no higher than 4.04uH, I can imagine, this is wrong, because I simulated with 4.7uH and all is OK, Phase Margin, Gain, Ripple...

Same happen with Sense Resistor, Webench doesnt recomend to me, values higher than 5mOhm, but when you calculate this one with the Ecuations you find in the Datasheet, I must use 6mOhm resistor.

Should I forget this limits? I can understand that the Webench is ver "conservative" related to this values...

  • 0
    TI__Expert 6860 points
    Carlos ,

    Yes you can use higher inductance ie 4.7uH for your application . On the Current sense calculation , my recommendation will be to add a slight margin on the OCP current limit value when you are calculating the Current sense resistor .

    --_Ambreesh