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:
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
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.