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WEBENCH® Tools/TPSM846C24: TPSM846C24 Webench error for feedback resistor

Raoul Tawel
Prodigy 105 points
Part Number: TPSM846C24

Tool/software: WEBENCH® Design Tools

I used Webench to design a 0.85V @30A power supply solution based on the TPSM846C24.

In my project, I requested a VOUT of 0.85V and the tools generated a schematic which I used to implement a board.

During testing, I found the output voltage close to 0.8V instead of 0.85V that I had requested.

Looking closer at the datasheet, I found a discrepancy between the value that Webench calculates for the feedback resistor \and the value given in the datasheet . Webench suggested a 15.4K resistors while the datasheet suggested a 14.3K resistor. Looking closer at other output voltages, there seems to be some correct values and a few incorrect values.

Looks to me that the Webench simulation engine for this part number is buggy. Please confirm.

  • 0
    TI__Mastermind 21755 points
    Hi Raoul,

    Thanks for the feedback.

    I checked that the calculated value in the tool is very close to 14.3k but selected resistance is higher which leads to lower Vout values so we will fix this issue. In this case, the tool should recommend 14.3k resistor for a 0.85V design.

    Regards,
    Amod
  • 0 in reply to Amod Vaze
    Prodigy 105 points
    For your information, as a test, I tried several voltages other then 0.85V and noticed that the webench tool gave incorrect values some of the times. So the issue needs to be fixed. Also, 14.3K resistors are readily available from Mouser and Digikey - so the Webench tool should be aware of this and not round off to the nearest value it thinks is available.
  • 0 in reply to Raoul Tawel
    TI__Mastermind 21755 points

    Thanks Raoul, we will fix the feedback design such that it works for all output voltages. The tool has access to the resistors but is picking the wrong value currently. You can see this issue by clicking on BOM and then "Select Alternate Part" for Rfbb component. In the recommended limits, click "Edit" and you can observe the target value is 14290. The selected value is higher though (15.4k). So, we will fix the min and max limits of the feedback resistor so it picks the correct value.

    Regards,

    Amod