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I have seen certain MOSFET data sheets with a negative threshold voltage, like:

  • Si2301DS Gate-Threshold Voltage \$V_{GS(th)}\$ = -0.45 V
  • AO4425 Gate-Threshold Voltage \$V_{GS(th)}\$ = -3.5 V

Does it mean the MOSFETs are depletion type? Does it mean that if I do not apply any gate voltage and pull the gate to 0 or ground, they will still conduct until it is made below -3.5 V? Can someone please explain?

I am looking for MOSFETs that will switch off when Li-ion cell voltage reaches 3.3 V or lower.

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They're PMOS. Vgs sign is opposite to NMOS. For a PMOS to conduct, Vgs has to be negative... Simple as that...

I am looking for MOSFETs that will switch off when Li-ion cell voltage reaches 3.3 V or lower.

You can get integrated LiIon protection chips to do that...

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  • \$\begingroup\$ but TP4056 module has a cutoff voltage of 2.5 V. I thought LI-Ion cells should not go below 3.5 V. TP4056 is the cheapest one. Do you have any other solution ? \$\endgroup\$
    – Srijib Mandal
    Commented Apr 12, 2017 at 14:16

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