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CSD25402Q3A (or similar) application

Other Parts Discussed in Thread: CSD25402Q3A, CSD75208W1015

We are trying to use the  CSD25402Q3A as bipolar switch (please see http://cds.linear.com/docs/en/datasheet/4417f.pdf, Fig1, M5, M6).

The input voltage is between 3 and 3.5V, gate drive is solid 0V. The current is between 0 and, say, 4A

It looks like M5 behaves very differently from M6. The combined (two MOSFETs) resistance is between 90 and 250mOhms (depending on input voltage). The lion share (~80-90%) of the voltage drop is across M5 (reverse biased part). 

Do you have any information about MOSFET behavior when it is reverse biased?

Thank you.

Michael Kogan

  • Michael, 

    The forward voltage drop across the MOSFET is characterized in Figure 9 of the datasheet. How much current are you pushing through the device? 

    We actually have some dual common source FET, the CSD75208W1015 chip scale part, but it is not capable of handling the levels of current that an SO-8 or SON3x3 device would be able to handle 

  • Hi Bret,

    Thank you for the prompt reply.

    We are trying to push up 5A peak through the device

    Figure 9 in the datasheet refers to the built-in diode voltage drop. The diode should be shorted/bypassed by fully biased MOSFET (if all goes well). It does not seem to go well in out case (MOSFETs connected back to back to form bipolar switch in single Li-Ion cell power path application). The reverse biased  device seems to be going into saturation region when current goes up.

    Hence my question:

    What are the saturation characteristics (like Fig2 here http://www.ti.com/lit/ds/symlink/csd25402q3a.pdf) of reverse biased MOSFET?

    Best regards

    Michael Kogan

    Brett Barr1 said:

    Michael, 

    The forward voltage drop across the MOSFET is characterized in Figure 9 of the datasheet. How much current are you pushing through the device? 

    We actually have some dual common source FET, the CSD75208W1015 chip scale part, but it is not capable of handling the levels of current that an SO-8 or SON3x3 device would be able to handle 

  • The saturation characteristics of the FET with a negative bias will be the same as the FET with a positive bias. Are you sure that Vgs is not being degraded by the negative drain to source voltage?