TC1267 pdf datasheet

The TC1267 is an application-specific, low dropout
regulator (LDO), specifically intended for use in PCI
peripheral card applications complying with PCI Power
Management (PCI 2.0). It provides an uninterrupted,
3.3V output voltage when the main (5V) or auxiliary
(3.3V) input voltage supplies are present.
The TC1267 consists of an LDO, a voltage threshold
detector, external switchover logic and gate drive
circuitry. It functions as a conventional LDO as long as
the voltage on the main supply input (VIN) is above the
lower threshold (3.90V typical). Should the voltage on
VIN fall below the lower threshold, the LDO is disabled
and an external P-channel MOSFET is automatically
turned on, connecting the auxiliary supply input to
VOUT, and ensuring an uninterrupted 3.3V output. The
main supply is automatically selected, if both the main
and auxiliary input supplies are present, and transition
from one input supply to the other is ensured glitchfree.
High integration, automatic secondary supply
switchover, Kelvin sensing, and small size make the
TC1267 the optimum LDO for PCI 2.0 applications.