Chippie, do you mean that the duty cycle is varied by adjusting the Vref and also voltage to pin 2? From what i get, if we slide the pot so that the voltage from vref to ground increase, the voltage at pin 2 to ground will decrease, and vice versa. This will simply adjust the duty cycle, am i right? Please correct me if i'm wrong.
I've seen a circuit which didn't use the pin 4 and 5 of this chip, however that circuit is intended for use with car audio amplifier. Is it ok if i simply ground these pins for motor speed controller?
About pin 6 and 7, from what i understand is that these pins are used as the switching frequency. From that circuit, it is using 4.7K resistor and 10nF cap. Using the equation 1/(Rt x Ct) yields the frequency as 21.3kHz. Divide it by 2 yields the frequency as 10.65 kHz (correct me if i'm wrong). The question is why the circuit use this frequency (10.65 kHz) ? Does it has anything to do with the remote control frequency or it's just depends on the designer of what frequency he want to use?