# Help reading a datasheet - MOSFET voltage drop?

Hi folks - trying to figure out what the rough voltage drop is going to be between drain and source on this mosfet:

Not exactly sure which datapoint I'm looking for...nothing seems immediately obvious...

Quick help?

Thanks!

From listed document:

RDS depends on current, varies between 0.18 - 0.26. Also see Figure 2.

Hope that helps.

Willem

“trying to figure out what the rough voltage drop is going to be between drain and source”

Worst case V = I * Rmax

If you know the current & resistance you can calculate the voltage ([u]Ohm’s Law[/u] says Voltage = Current x Resistance).

So for example, that’s about 1/4 of a volt at 1 Amp. (That’s assuming the MOSFET is fully-saturated… Turned fully-on.)

BTW - You can calculate power (related to heat) as Watts = Voltage x Current… A MOSFET with lower RDS will drop less voltage and run cooler (in a switching application where it’s either fully-on or fully-off).

Willem43:
RDS depends on current, varies between 0.18 - 0.26. Also see Figure 2.

No, it doesn’t really depend on current, it depends on the individual device(*), the gate-source voltage and the temperature. MOSFETs that are turned on act as fairly good resistors so long as the source-drain voltage
remains small (which ought to be the case unless you are vastly overloading it)

The datasheet says that with 5V gate drive all devices will have Rds(on) <= 0.22 ohms at 25C, and the graph
in Fig 4 can be used to convert that for other temperatures.

(*) All MOSFETs have significant process variation in parameters related to gate voltage, and furthermore
will change with age - use the worst case values from the datasheet only… The typical values as displayed
in the graphs are typical, not universal.

Thanks so much folks - perfect info. Really appreciate it.