By providing primary-side control, the device eliminates the requirement for opto-couplers and secondary-side control circuitry, reducing component count, board space requirements and cost. Primary-side regulation results in higher efficiency with less heat generated in the power supply, which increases reliability. Additional benefits include improved output voltage and current accuracy, enhanced over-voltage and short-circuit protection, and better EMC performance, achieved by frequency dithering.
The AP3988 switcher regulates output voltage using piece-wide pulse frequency modulation, in which analog levels are represented as fixed-duration pulses of varying repetition rate. Transistors with 700VCBO are built into the device and start-up current is typically 0.2 µA.
The switcher has integral cable voltage drop compensation of 5% of nominal voltage and adjustable line voltage compensation.
The AP3988 controller is designed for use in 5.5W adapters and is offered in the SO-7 package.