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WEBENCH® Tools/LM2735YMYEVAL: wrong results in Webench design

pradnya bapat
Prodigy 10 points

Part Number: LM2735YMYEVAL

Tool/software: WEBENCH® Design Tools

Tried this circuit on webench it is giving wrong values for the inductor and output capacitor, compared to the examples in the data sheet are look ok

Design inputs

Device LM2735Y

Input Min 5 Max 5.5V

Vout 18V

Vout Current 0.025A

  • 0
    TI__Expert 8365 points

    Hi Pradnya,

    We will review the inductor and capacitor selection and get back to you on this.

    Thanks & Regards,
    Praveen

  • 0 in reply to Praveen Badiger
    TI__Expert 8365 points

    Hi Pradnya,

    we have reviewed the component selection for this device. It has been observed that minimum inductor selection on WEBENCH is done as per datasheet as shown below expect datasheet consider 10%-30% of full load current as a maximum ripple. whereas WEBENCH considers 30% of input current as a maximum ripple to get more accurate selection. 

    The minimum/ maximum inductor limits are calculated and WEBENCH selects the suitable inductor within a given range.

    The minimum output capacitor is selected based upon the desired output ripple and transient response as per the datasheet. However, WEBENCH also checks the stability for the given condition(VinMin, VinMax, Vout, Iout) and increases the value of the output capacitor to satisfy the minimum stability criteria(Phase Margin>45 deg). There was a bug in the algorithm and hence output capacitor was getting selected as 2.47F. We have fixed this bug now. However, please note that minimum stability criteria do not satisfy for the above condition and WEBENCH fails to create a design. 

    The changes will be reflected on ti.com by mid of September.

    Thanks & Regards,

    Praveen