WEBENCH® Tools/LMR36506: Webench Design update failed at 0.130A

Mark Ackerson

Part Number: LMR36506

Tool/software: WEBENCH® Design Tools

Customer ran into an issue with LMR36506 Webench design when changing operating current to 0.130A:

https://webench.ti.com/appinfo/webench/scripts/SDP.cgi?ID=FF083AE140DE0DD2

When operating current is reduced to 0.130A, Webench flags an error "Design update failed. This design is not stable due phase margin either smaller than 35 or greater than 120."

Please advise.

Thanks,
Mark

over 5 years ago

0 Harrison Overturf over 5 years ago

TI__Genius 10820 points

Hello Mark,

I believe what's happenng here is that that because you initially input 0.14A for Iout max, then Webench will calculate the inductor current ripple based on this value of Iout. So if Webench calculates the inductor current ripple at 40% of Iout=0.14A, then this value may be too small for the internal slope compensation of the device leading to Webench thinking the design is unstable.

I recommend selecting the inductor based on Iout=0.6A, and then simulate using Iout=0.13A. Below I've attached my design, try this out and let me know if this gives you the same error or not.

https://webench.ti.com/appinfo/webench/scripts/SDP.cgi?ID=90AA71314FA08BAD

Regards,

Harrison Overturf