Proper configuration of a PWM fan which should be stopped when the controller power is cut off

Question

Recently I am working on a controller to drive a PWM fan (datasheet). I am using a atmega32u4 and it sends a 25khz PWM signal to the fan and it's working well. I want the fan to be off when I cut the power to the controller, so I added a pull down resistor like below:

So my questions are:

1. is the choice of the pull down resistor correct? It pulls down the PWM control to 0.52V (need to be less than 0.8V according to the data sheet) when the atmega32u4 is powered off. OTOH when the atmega32u4 is on, it pulls down the high signal from D3 from 5V to 4.8V

2. do i need to add a diode in front of D3? Will it be considered harmful if there's possibility a current flowing back from the PWM control wire to D3 when the atmega32u4 is off?

I am a newbie to electronic and I want to learn how to make my circuit correct and safe. Will be very grateful if my questions can be answered.

Answer 1

Have a look at the below corrected diagram . 1). You should add a freewheeling diode at the motor terminal to catter inductive kicks. 2)If you need further protection you can isolate the microcontroller section from the MOSFET via an optocoupler, and there power supplies respectively. 3) Add a zener at the base of the Mosfet to protect the gate at what ever, voltage you are operating the FET.You may also try adding an inverter stage to switch off the FET on power off. @Ivan ,I missed your datasheet anyways, Try using an inverter in between D3 and rest of the ckt of yours. Sometyhing like this;