calculating the bootstrap capacitor value

[sabrahermassi]

hello!
i was calculating the bootsrap capacitance value of a mosfet driver IR2101 and i was wondering what the operation frequency f means ???
I couldn't find it in the datasheet of the IRF2101 .. well i'm using a mosfet IRF7739l too. can someone help me please in order to calculate the Cboot value needed for my allpication .
i want to drive a brushless motor using STM32F1 microcontroller !!

 

[btbass]

f might be the frequency of the pwm your driving it with. A typical frequency is 16KHz. Not audible to most people.
Any value from 100n to 470n should work ok.

 

[sabrahermassi]

I calculated the PWM frequency of my brushless motor using this equation : PWM= [Kv*V*poles]/20 and i found 10Khz . As i know that there is a rule which say that the PWM frequency should be at least 10 times that of maximum frequency of the motor. doeas this mean that i have to choose an operating frequency of 100Khz ??

 

[btbass]

I have never heard of that rule or seen that formula?
You can drive the motor with what ever pwm frequency you like.

 

[sabrahermassi]

Should I choose a PWM 's duty cycle of 50% or more in order to drive my motor ?

 

[btbass]

You use the duty cycle to control the speed of the motor.
Changing duty cycle changes motor speed.