arduinomosfetpwm
The V(GS) Gate to Source Threshold Voltage for a MOSFET I would like to use is listed as Min 1.5, Typ 1.9, and Max 2.3V. I am working with a Teensy3.1 that outputs 3V on the PWM pin. Do I need to get this voltage in proper range for this MOSFET, and how should I do this?
The datasheet for the MOSFET can be found here: CSD18534KCS 60V.
Read your own question. The answer is obvious since it is embodied in the question.
You said yourself the gate threshold voltage is 2-4 V according to the datasheet. So how can 3.3 V on the gate possibly guarantee that the device is on? Clearly 3.3 V is less than 4 V.
You should also look more closely at what gate threshold really means. Note that it defines "gate threshold" as the gate voltage at which there will be 250 µA of drain current. That's unlikely to be a useful amount of current in your application, and is certainly not in any way the fully on state of the MOSFET.
Gate threshold is not a useful parameter if you want to turn the FET fully on. It tells you where it starts to turn on, not what it takes to turn it on fully, or full enough for your application.
The drain to source on-resistance is much more relevant, just a few lines in the datasheet below the threshold voltage. That is specified as 540 mΩ, but at 10 V on the gate. In other words, this FET is intended for 10 V gate drive to really want to turn it on. They aren't making any promises what happens between the threshold voltage and 10 V.
If you want to drive a FET with only 3.3 V on the gate, you have to get one specified for that. For example, the IRLML2502 is characterized at low gate voltages. The datasheet promises the Rdson will be 80 mΩ or less at 2.5 V on the gate, and 45 mΩ or less at 4.5 V. So one of those can be usefully driven from 3.3 V. In that case you know it won't exceed 80 mΩ and can support up to 3.6 A.
International Rectifier datasheets are never obvious with their pin labels. They hide them in the engineering drawings of the packages.
For instance, the TO-220 package, on page 9 of the datasheet, has this drawing:
The pins are numbered 1-3 and the tab numbered 4. To the right of that drawing is a little table:
LEAD ASSIGNMENTS
- GATE
- DRAIN
- SOURCE
- DRAIN
The other packages are even less clear with the table being in tiny text hidden somewhere in the drawing.
The "max" threshold isn't the upper limit for the gate voltage - it's the upper limit of the threshold voltage - the voltage above which you should be to turn it on. The threshold itself could be anywhere between MIN and MAX. As long as you are above MAX then you are good.
Best Answer
Not to worry. The gate threshold voltage is simply the level required to make sure the device switches. In this case, in can be as high as 2.3 volts, so your 3 volt PWM output is just about right.
This represents a minimum gate voltage that you need to apply. For the maximum, look at page 1 of the data sheet, "Maximum Ratings". The second item is Vgs, gate-source voltage. At +/- 20 volts, you have nothing to worry about.