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Mosfet application doubt

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Veketti:
Dear All,

This is most likely stupid guestion, but I'll ask anyway to be sure. For example IRLML6344 chart "Typical output characteristics" have line for 4.5V Vgs but it is plotted to at around Vds = 0.5V. So the guestion is, if I have Vds = 12V and Vgs = 5V is it out of its operating range? My assumption is that it is ok as long as the Vds < 30V and Vgs < 12V it's ok.

Second guestion is, why didn't they plot it any further if it is ok to be operated with higher Vds Vgs combo?

TimFox:
The curves for high VGS are truncated because the drain current is too high for higher VDS at higher gate voltage.

Veketti:
Excellent, makes sense. So the conclusion is that Vds = 12V and Vgs = 5V is perfectly fine as long as the Id is within limits (<4A for continuous current)?

Just a side note. Maybe the Id 5A and 4A are wrong way around. Now higher current is lower temperature.

fourfathom:

--- Quote from: Veketti on September 25, 2023, 07:38:45 pm ---Excellent, makes sense. So the conclusion is that Vds = 12V and Vgs = 5V is perfectly fine as long as the Id is within limits (<4A for continuous current)?

--- End quote ---

No.  If you have a Vds of 12V and and an Ids of 4A that means the transistor is dissipating 48 Watts.  This is not going to end well for that tiny SOT-23 package with its specified maximum power dissipation of about 1W.

How do you plan to use this FET?  Typical applications are low-power linear or higher-current switching (where the Vds is near zero when current is flowing).

magic:

--- Quote from: Veketti on September 25, 2023, 07:38:45 pm ---Excellent, makes sense. So the conclusion is that Vds = 12V and Vgs = 5V is perfectly fine as long as the Id is within limits (<4A for continuous current)?

--- End quote ---
This means "never", because drain current will be tens of amps if Vds=12V and if it's limited to 4A then drain voltage will be very low (4A ยท RDS(on)).

This plot applies to linear operation, with simultaneous high voltage and not negligible current through the FET.

You are probably considering switching. When you switch the FET on, external load limits current and then Vds becomes very low. If the load fails to limit current (e.g. shorts out) then you end up in the uncharted corner (high Vds, high Vgs) and the FET doesn't survive for long.