The LTC1436A/LTC1437A are synchronous step-down switching regulator controllers that drive external N-channel power MOSFETs in a phase lockable, fixed frequency architecture. The Adaptive Power™output stage selectively drives two N-channel MOSFETs at frequencies up to 400kHz while reducing switching losses to maintain high efficiencies at low output currents.An auxiliary 0.5A linear regulator using an external PNP pass device provides a low noise, low dropout voltage source. A secondary winding feedback control pin (SFB) guarantees regulation regardless of the load on the main output by forcing continuous operation.An additional comparator is available for use as a lowbattery detector. A power-on reset timer (POR) is included which generates a signal delayed by 65536/fCLK(300ms typically) after the output is within 5% of the regulated output voltage. Internal resistive dividers provide pin selectable output voltages with remote sense capability.The operating current level is user-programmable via an external current sense resistor. Wide input supply range allows operation from 3.5V to 30V (36V maximum).ApplicationsNotebook and Palmtop Computers, PDAsCellular Telephones and Wireless ModemsPortable InstrumentsBattery-Operated DevicesDC Power Distribution Systems