9.3.7 PWM Generator

Maximum duty cycle is higher for these devices than for their UC384x predecessor. This is primarily due to the higher ratio of timing capacitor discharge to charge current, which can exceed one hundred to one in a typical BiCMOS application. Attempts to program the oscillator maximum duty cycle much below the specified range by adjusting the timing component values of R_T and C_T must be avoided. There are two reasons to stay away from this design practice. First, the ICs high discharge current would necessitate higher charging currents than necessary for programming, defeating the purpose of low power operation. Secondly, a low-value timing resistor prevents the capacitor from discharging to the lower threshold and initiating the next switching cycle.