GENERAL DESCRIPTION
The outputs are both rated for up to 1A. Both outputs are adjustable using external resistors. The step-down converters operate at 1.3MHz fixed switching frequency under normal load and in a pulse skipping mode for light loads. The switching clock is shifted 180° for SW2. The E/S pin provides an enable function and allows the converter to be synchronized to an external clock. With E/S held low, the AP3421/A/B draws less than 10µA current. In the start-up sequence, the VO1 output is designed to precede the VO2 output. The two outputs have controlled start-up sequence. Power On Reset (POR) function is provided by means of an open-drain output present on the POR pin. The POR function monitors VMON, FB1 and FB2, and pulls low if any of these begin to drop out. The POR is internally deglitched and provides a delayed recovery/reset time. The AP3421/A/B provides peak over-current protection, short circuit protection and thermal shutdown. Discharge-Before-Turn-On discharges the outputs completely before soft-starting to always bring them up in the proper sequence at start-up or after a POR (For AP3421/A only).
BCD Semiconductor Manufacturing Limited
