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WEBENCH® Tools/LMS3655-Q1: Vin Min is high

Prodigy 40 points

Replies: 4

Views: 119

Part Number: LMS3655-Q1

Tool/software: WEBENCH® Design Tools

When simulating LMS3655AQRNLRQ1 in WEBENCH with Vout=5.05, 4.5A then the minimum allowed Vin is 6.7V.
According to the datasheet it should be around 5.5V.

Why is the VinMin so high in WEBENCH?

I am using the 'High Efficiency Design' option.

Best regards
Kim

  • Hi Kim,

    This device has a maximum duty cycle limit of 98%. For the above condition, the maximum duty cycle is being hit (minimum off time 65ns). The duty cycle on WEBENCH is calculated considering the voltage drop across the inductor DCR and Rdson of the high side and low side MOSFETs.Please either reduce the Vout or increase the input Voltage.

    Thanks & Regards,
    Praveen B

  • In reply to Praveen Badiger:

    Hi Praveen

    Thanks for your answer.

    The datasheet suggests running at 5.6V (see highlighted):

    7.7 System Characteristics:

    When changing my test condition to match (3.5A) it could go down to 6.3V but I am still puzzled about the difference (5.6V in datasheet and 6.3V in WEBENCH). Are datasheet 'test conditions' calculated using ideal components rather than real life tests?

    Best regards
    Kim

  • In reply to Kim Sivebaek1:

    Hi Kim,

    The design should be created for Vmin=5.6V as per the datasheet for the given components(Non-ideal) and test conditions. We have fixed this issue. You will able to create the design for Vmin-=5.7V since different components are selected on WEBENCH( Variation of Rdson and DCR values). The fix will be available on ti.com by mid of the next week. We will keep you updated on the same.

    Thanks & Regards,

    Praveen B

  • In reply to Praveen Badiger:

    Hi Kim,

    The fix is available on ti.com

    Thanks & Regards,

    Praveen B