I am driving a MOSFET with AVR using PWM for controlling a motor. I have a 4K7 pull-up resistor on the gate. My question is, do I need a resistor in between the AVR pin and the gate? (The mosfet is NX2301P)
Electronic – AVR and MOSFET gate resistor
avrdrivermicrocontrollermosfet
Related Solutions
It is generally a good idea to include a gate resistor to avoid ringing. Ringing (parasitic oscillation) is caused by the gate capacitance in series with the connecting wire's inductance and can cause the transistor to dissipate excessive power because it doesn't turn on quickly enough and hence the current through drain/source in combination with the somewhat high'ish drain-source impedance will heat the device up. A low ohm resistor will solve (dampen) the ringing.
As @PhilFrost mentiones, a high value resistor to ground is a good idea to avoid capacitive coupling driving the transistor when it is otherwise not connected.
simulate this circuit – Schematic created using CircuitLab
At all times keep the wiring between logic output, transistor gate, transistor source and ground as short as possible. This will ensure fast turn on/off.
It's right there, in section 21. See it?
\$\frac{0.25\text{V}}{10\text{mA}}= 25\Omega\$
\$\frac{5\text V - 4.75\text{V}}{10\text{mA}}= 25\Omega\$
Therefore yes, the output has a resistance of 25\$\Omega\$ at 25\$^{\circ}\$C.
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Best Answer
No you do not need a series resistor. If you put one in there it would limit the current a bit and might help in case of some layout issue, but it's not necessary.
Why the rather low gate pull down and why a pull down rather than pullup? Normally I'd expect to see more like a 20K pullup so if the AVR output is high impedance the motor turns off. A pull down resistor on a P-channel MOSFET gate means that the motor will turn on if the input is open.