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WEBENCH® Tools/LM27403: WEBENCH design suggestion for 3.3v to 0.9v converter with 8.4A load

Part Number: LM27403
Other Parts Discussed in Thread: CSD17312Q5, CSD17311Q5

Tool/software: WEBENCH® Design Tools

Hi all,

Somehow the webench suggested a converter design based on the LM27403 with two power FETs - CSD17312Q5 (lower FET) and CSD17311Q5 (Higher FET).

While looking at the webetch simulation it can be noticed that the SW terminal goes below -0.3v (it absolute maximum/minimum voltage) - (about -0.95v at the skew time).

This negative voltage value is apparently caused by the CSD17312Q5 "parasitic-diode".

Please update if that voltage will harm the controller (LM27403)?

If it will, please update me and the webench suggestions (regarding the reverse parasitic-diode voltage).

And if not, please note, how should I refer to the data-sheet "Absolute Maximum Ratings"?

Regard,

Alon Blumenfeld

  • Hello Alon,

    WeBench only simulates the forward voltage drop of the MOSFETs parasitic body diode during the dead time period, The simulation for this is relatively basic in terms of what you will actually get on the bench with parasitic's and all.  For this type of accuracy we suggest measuring on the bench and measuring at the GND pin to Switch at the device with a very short ground connection.