i have set up the circuit, but i do have some problem that i can't figure it out.. my frequency requirement is 20khz, i do follow the formula that the data sheet given, base on my oscilloscope, it shown 10khz.. capacitor voltage is 0.01 micro. resistor value is 5.5k ohms. when i connect the the potentiometer, i can't adjust the duty cycle at all.. I have attach my circuit output oscilloscope result. circuit that i set up and datasheet, it content the formula that i use.. data sheet for TL594 please give me some advice on this..