Webench simulation curves mismatch

Francois Fortin

Prodigy 20 points

Other Parts Discussed in Thread: LM3150

I have a design that has a 2.8A inductor ripple current with a 5.0V output à 8A.

The simulation report indicate expected values but the simulation waveforms do not fit that.

For example Vout oscillates between 5.30 and 5.40V and IL oscillates between 7.6 and 8.4A.

What should we understand from the simulation waveforms?

Thank you

over 9 years ago

0 Wanda Garrett - WEBENCH Design Center over 9 years ago

TI__Intellectual 2360 points

Hi Francois,
So we can investigate further, please provide the regulator part number and your design inputs (Vin Min, Vin Max, Vout, Load).

0 Francois Fortin over 9 years ago

Prodigy 20 points

HI Wanda,
here are the parameters: LM3150, Vin 22-26V, Iout 8A, Vout 5V

0 Wanda Garrett - WEBENCH Design Center over 9 years ago in reply to Francois Fortin

TI__Intellectual 2360 points

Hi Francois,

Thanks for the information. I'm checking into this now to see what's causing the discrepancy.

0 Wanda Garrett - WEBENCH Design Center over 9 years ago in reply to Wanda Garrett - WEBENCH Design Center

TI__Intellectual 2360 points

As a constant On-time converter, the LM3150 switching frequency is extremely sensitive to output ripple. When the output capacitor's ESR is large (over about 30-40mohm), it can be the major contributor to output ripple; as ripple increases, frequency increases, pushing the ripple back down again. In this case, with ESR=100mOhm, it appears the PSPICE model responds a little differently than the calculations do. We see the modeled switching frequency rising to around 1MHz and output ripple is around 65mV, while the calculated switching frequency is much lower and output ripple is much higher. If you change Cout to have lower ESR, the matching is greatly improved. I choose Cout with ESR of 12mOhm (instead of 100mOhm) and found the calculated ripple to be 30mV compared to simulation results of 24mV - fairly close for this situation.

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Webench simulation curves mismatch