WEBENCH® Tools/LM61460-Q1: Unable to simulate with 2.1MHz operation

Jared Becker

Genius 11845 points

Part Number: LM61460-Q1

Tool/software: WEBENCH® Design Tools

Hi Team,

I am trying to simulated the LM61460-Q1 under the following conditions:

Vin: 9V - 19V

Vout: 5V

Iout: 4A

Ambient Temp: 30

When I switch to 2.1MHz switching frequency, the design will not update due to lack of phase margin. Can I know what the phase margin is under those conditions? I am surprised the phase margin is so low since those operation conditions seem fairly reasonable. Are there any conditions where 2.1MHz operation is acceptable?

Thank you,

Jared

over 5 years ago

0 Amod Vaze over 5 years ago

TI__Mastermind 26740 points

Jared,

Thanks for your question. I was able to reproduce the same issue as well. I did some initial debugging and it seems we might need to double check the Cout and Cff calculations to ensure the design is stable especially since this device is internally compensated. In addition, we are not taking into account the effect of Rff on the pole/zero locations currently. The tool is estimating around 28 degrees of phase margin and hence failing for 2.1MHz design. The team will take a look and keep you updated on the status of this issue.

Regards,

Amod