LM3481: Bode plot, PSpice for TI

Kurumi Hasegawa

Part Number: LM3481
Other Parts Discussed in Thread: LM5155

Hi team,

I’m trying to get bode plot using LM3481 average model in PSpice for TI, as referring to this E2E. I’m planning to have DAC-programmable output in the range of 2.5V~15V in SEPIC configuration.

For Vout=15V or 8.75V, it worked as expected. But when I check bias voltage on COMP with Vout=2.5V setting, it showed negative value. Does this model have limitation for Vout? If it has, could you share min Vout value acceptable?

Best regards,

Kurumi

9 months ago

0 Bryan Radix 9 months ago

TI__Intellectual 2790 points

Hi Kurumi,

Thanks for reaching out.
I've already calculated the duty cycle at Vin=5V, Vout=2.5V and it's about 0.39, so not above the maximum duty cycle.

I'll get back to you once I've looked at other possible causes.

Thank you and best regards,
Bryan

0 Niklas Schwarz 9 months ago in reply to Bryan Radix

TI__Mastermind 21010 points

Hi Kurumi,

Thank you very much for your patience.
I think the problem with this average model simulation is the topology.
The LM3481 avg model is build for Boost topology. If I read your description correctly, you are building a SEPIC design.
If the calculation are meant for a SEPIC, this Boost average model may not give accurate simulation data.

Unfortunately, we do not have a PSpice average model for SEPIC designs.

I am very sorry for this inconvenience.
Best regards,
Niklas

0 Kurumi Hasegawa 9 months ago in reply to Niklas Schwarz

TI__Expert 6601 points

Hi Niklas,

Understood, thank you so much for checking. And yes, I'm building SEPIC design.

I'm observing similar phenomena for LM5155-Q1DSS_AVG model as well. Would you happened to know if LM5155-Q1DSS_AVG is build for boost topology?

Best regards,

Kurumi

+1 Niklas Schwarz 9 months ago in reply to Kurumi Hasegawa

TI__Mastermind 21010 points

Hi Kurumi,

The default testbench for our PSpice average models is always for Boost topology.
This is also the case for LM5155.

However, for LM5155 we have calculation tools available that calculate the bode plot based on the design parameters.
This quickstart calculator is also available for SEPIC topology:
https://www.ti.com/tool/download/SNVR481

Best regards,
Niklas

0 Kurumi Hasegawa 9 months ago in reply to Niklas Schwarz

TI__Expert 6601 points

Hi Niklas,

Understood on LM5155. Thank you again for your support.

Best regards,

Kurumi

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LM3481: Bode plot, PSpice for TI