WEBENCH® Tools/TPS54160: Operating Values and steady state simulation values are not matching

Vigneshwaran Gurusamy

Part Number: TPS54160

Tool/software: WEBENCH® Design Tools

Hi,

I want to bring to your notice that there is discrepancy in output voltage ripple obtained from op Vals and steady state simulation of TPS54160.

The design of TPS54160 is in shared link.

To identify which one (op vals or simulation) is appropriate, I have performed calculation based on equation 17 of http://www.ti.com/lit/an/slva630a/slva630a.pdf.

The calculated values are matching well with the op values and the calculations are in attached excel file.

Are they (op vals and simulation) not supposed to give same result?

When I checked with default design of TPS54160, there is no significant difference in values of op vals and simulation. The variation is observed after changing some of BOM components.

Vout ripple_E2E.xlsx

Please let me know where the issue is.

Thanks and Regards

Vignesh

over 9 years ago

0 Maqboolahmad Modinnavar over 9 years ago

TI__Prodigy 220 points

Hi Vignesh,

Ideally Opvals and Simulation results match. But practically, these values may have a difference and generally the variation is between 0 to 3% what we observe.

Coming to this device, the discrepancy that you are observing might be due to following reasons.

1. The values of simulation results shown under Performance summary for Vout ripple is the average value of Vout ripple, considering all the cycles displayed in the simulation window. This will be close but to get more accurate value you can use the Marker option to measure the Vout ripple.

2. The design created is for fsw=250kHz, but if you see the actual fsw in simulation results, it is bit lesser than that. This small difference in fsw may increase Inductor current ripple and hence the Vout ripple.

Thanks.

Regards,
Maqbool

0 Vigneshwaran Gurusamy over 9 years ago in reply to Maqboolahmad Modinnavar

Intellectual 260 points

Hi Maqbool,

Thanks for the quick response.

1. I have obtained the vout ripple from both performance summary and marker. Vout ripple obtained from performance summary is closer to the value obtained from marker in most of the cases. Pl find the attached excel file for your reference. The error between Vout ripple of op val and marker value is ranging from 7% to 28%.

0247.Vout ripple_E2E.xlsx

2. Variation in fsw is about 1 to 2%. I doubt whether it causes variation of more than 10% in Vout ripple.

Thanks and Regards

vignesh

0 Gerold Dhanabalan - High Performance Radar over 9 years ago in reply to Vigneshwaran Gurusamy

TI__Genius 14455 points

Hi Vignesh,

The Vout ripple equation used in WEBENCH is much more accurate than the one that you have calculated using the equation in the excel. the WEBENCH values matching with the SPICE models is a good confirmation on the accuracy.

Regards,

Gerold

0 Vigneshwaran Gurusamy over 9 years ago in reply to Gerold Dhanabalan - High Performance Radar

Intellectual 260 points

Hi Gerold,

Thanks for the response.
Does it conclude that Vout ripple from Webench simulation results are accurate than the one from operating values ?

Regards
Vignesh

0 Gerold Dhanabalan - High Performance Radar over 9 years ago in reply to Vigneshwaran Gurusamy

TI__Genius 14455 points

Vignesh,
What I saw in the spreadsheet was sim results matched the operating values closely. The calculated results using the excel equation was not matching.
Regards,
Gerold

0 Vigneshwaran Gurusamy over 9 years ago in reply to Gerold Dhanabalan - High Performance Radar

Intellectual 260 points

Hi Gerold,

Actually it is other way around. Equation based calculated values matches with operating values where as operating values are not matching with sim results. That is why I brought the issue to E2E.

Regards
Vignesh

0 Gerold Dhanabalan - High Performance Radar over 9 years ago in reply to Vigneshwaran Gurusamy

TI__Genius 14455 points

Hi Vignesh,
In terms of percentage difference it looks 28% as the max difference. But in terms of absolute voltages it is only 5mV. I would go with the simulation results if you are too specific.
Regards,
Gerold

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WEBENCH® Tools/TPS54160: Operating Values and steady state simulation values are not matching