Designing a MOSFET circuit for low pass filtered PWM operation and with saftey considerations

I am designing a circuit at the moment and, as part of that, I need to be able to run 4 12VDC fans (which i will run in parallel) with an operating current of 150mA and a starting voltage of 4.5V. My problem is that my supply rail is 24V.

At the moment I am thinking of using a 5V PWM signal from my microcontroller to control the gate voltage of a MOSFET. With a 50% duty cycle, I should achieve an average votage of 12V. However, PWM is noisy and it would be nice to be able to smooth the output voltage with a Low pass filter. It would be nice to put the filter between the micro and the MOSFET gate, I just have to make sure that the gate voltage is above the threshold voltage.

Here's my question: is something like this suitable? Also, how do I protect against anything that might go wrong? For example, if the fans short etc, I don't want to start a fire if the MOSFET is dissipating high amounts power.

Here's my thought process for choosing the MOSFET

• \$V_{GS(th)}\$ = \$0.67 V\$ which is greater than the expected 'off' voltage from my PWM pin


• \$V_{GS(max)}\$ is \$8V\$ which is less than my \$5V\$ max PWM output


• Max continuous drain current is \$6.3A\$ which is greater than my 4 fans ( \$4 \cdot 0.15 = 0.6A\$)


• With \$V_{GS}\$ at 2.5V (5V at 50% duty) I can supply over 20A. I don't understand this bit because the datasheet says a max Drain current of 20A pulsed. I guess that I can only do this for a very short amount of time?)
  
  
  
  • Max \$V_{DS}\$ is 30V, greater than my 24V
  
  
  • \$R_{DS(on)}\$ is typically 0.038Ohms at 4.5V gate voltage. At (\$4\cdot 150mA =\$) 600mA power dissipation is 22.8mW which I guess is low enough.
  
  
  
  

Here's my Schematic. What can I do to improve it and/or protect against anything that might go wrong?