DESCRIPTIO U
The LTC®1267 series are dual synchronous step-down switching regulator controllers featuring automatic Burst ModeTM operation to maintain high efficiencies at low output currents. The LTC1267 is composed of two separate regulator blocks, each driving a pair of external complementary power MOSFETs at switching frequencies up to 400kHz. The LTC1267 uses a constant off-time current mode architecture to provide constant ripple current in the inductor and provide excellent line and load transient response.
A separate pin and on-board switch allow the MOSFET driver power to be derived from the regulated output voltage,providingsignificantefficiencyimprovementwhen operating at high input voltage. The output current level is user-programmable via an external current sense resistor.
The LTC1267 series is ideal for applications requiring dual output voltages with high conversion efficiencies over a wide load current range in a small amount of board space.

FEATURES
■ Dual Outputs: 3.3V and 5V, Two Adjustables or Adjustable and 5V
■ Wide VIN Range: 4V to 40V
■ Ultra-High Efficiency: Up to 95%
■ Low Supply Current in Shutdown: 20mA
■ Current Mode Operation for Excellent Line and Load Transient Response
■ High Efficiency Maintained Over a Wide Output Current Range
■ Independent Micropower Shutdown
■ Very Low Dropout Operation: 100% Duty Cycle
■ Synchronous FET Switching for High Efficiency
■ Available in Standard 28-Pin SSOP

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