TOPSwitch is a self-biased and protected linear control current-to-duty cycle converter with an open drain output. High efficiency is achieved through the use of CMOS and the integration of the maximum number of functions possible. CMOS process significantly reduces bias currents as compared to bipolar or discrete solutions. Integration eliminates external power resistors used for current sensing and/or supplying initial start-up bias current. During normal operation, the duty cycle of the internal output MOSFET decreases linearly with increasing CONTROL pin current as shown in Figure 4. To implement all the required control, bias, and protection functions, the DRAIN and CONTROL pins each perform several functions as described below. Refer to Figure 2 for a block diagram and to Figure 6 for timing and voltage waveforms of the TOPSwitch integrated circuit.
