DESCRIPTION
The LTC ®1538-AUX/LTC1539 are dual, synchronous stepdown switching regulator controllers which drive external N-channel power MOSFETs in a phase-lockable fixed frequency architecture. The Adaptive PowerTM 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.

FEATURES
■ Maintains Constant Frequency at Low Output Currents
■ Dual N-Channel MOSFET Synchronous Drive
■ Programmable Fixed Frequency (PLL Lockable)
■ Wide VIN Range: 3.5V to 36V Operation
■ Ultrahigh Efficiency
■ Very Low Dropout Operation: 99% Duty Cycle
■ Low Dropout, 0.5A Linear Regulator for VPP Generation or Low Noise Audio Supply
■ Built-In Power-On Reset Timer
■ Programmable Soft Start
■ Low-Battery Detector
■ Remote Output Voltage Sense
■ Foldback Current Limiting (Optional)
■ Pin Selectable Output Voltage
■ 5V Standby Regulator Active in Shutdown: IQ < 200µA
■ Output Voltages from 1.19V to 9V
■ Available in 28- and 36-Lead SSOP Packages

APPLICATIONS
■ Notebook and Palmtop Computers, PDAs
■ Portable Instruments
■ Battery-Operated Devices
■ DC Power Distribution Systems