LDOs’ Transition Between Input Sources Is Glitch-Free

Intended for use in PCI peripheral cards such as NICs and PCMCIA cards, the TC1266 Smart LDO is designed to provide an uninterrupted 3.3V output from a 5V main or 3.3V auxiliary supply. The new low-dropout regulator monitors the 5V input while providing a tightly regulated 3.3V output at 200 mA. Consisting of an LDO, a voltage threshold detector, external switchover logic, and gate-drive circuitry, the TC1266 functions as a conventional LDO as long as the main voltage (V_IN) is above its lower threshold (3.90V typ.). Should V_IN fall below the threshold, the LDO is automatically disabled and an external P-channel MOSFET is turned on, connecting the auxiliary supply input to V_OUT, thereby ensuring an uninterrupted 3.3V output. The main supply is automatically selected when both main and auxiliary supplies are present, thus guaranteeing glitch-free transitions when going from one supply to the other.