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CSD87352Q5D: Saturation curve for Vds/Ids only showing ohmic region?

AR
Prodigy 30 points
Part Number: CSD87352Q5D

Tool/software:

Hello,

I am looking at calculating more accuratly the efficiency of a syncronous buck converter using the CSD87352Q5D NexFET design by looking at the SLVAEQ9 Application Report. To calculate the switching loss on high side mosfet, Vpl and Vgs(th) are calculated and are to be inserted into switch loss formula later on.

Now in the Application Report, ch. 3.1 shows eq. 21-24 and how to calculate Kn and Vgs(th) by using values from Figure 7. Now when i look at CSD87352Q5D mosfet the same curve does not show the saturation region for this particular mosfet (and i have seen more of them that dont show this. The image on left side shows this curve).  The image on the right side shows the same curve from the Application Report. 

How can i calcualte Kn and Vgs for CSD87352Q5D? 

Thx

  • 0
    TI__Mastermind 35530 points

    Hello AR,

    Thanks for your interest in TI FETs. Unfortunately, the saturation curves in the datasheet only extend out to VDS = 0.4V for the high side FET and to VDS = 0.2V for the low side FET. I believe this is due to current limitation of the tester used to generate these curves. I used the PSpice model to generate IDS vs. VDS curves for the high side and low side FETs.

    High side FET: VGS1 = 4.5V, ID1 = 79A, VGS2 = 4.5V, ID2 = 60A

    Low side FET: VGS1 = 4.5V, ID1 = 155A VGS2 = 4.5V, ID2 = 123A

    Please review and let me know if you need additional information. I am also including a link below to an app note for calculating power loss including common source inductance.

    https://www.ti.com/lit/pdf/slpa009

    Best Regards,

    John Wallace

    TI FET Applications