DESCRIPTION
The LTC®3541-3 combines a synchronous buck DC/DC converter with a very low dropout linear regulator (VLDOTMregulator) and internal feedback resistor networks to provide two output voltages from a single input voltage with minimum external components. When configured for dual output operation, the LTC3541-3’s auto start-up featurewillbringthe1.575VVLDO/linear regulator output into regulation in a controlled manner prior to enabling the 1.8V buck output with out the need for external pin control. The 300mA VLDO/linear regulator output will source only 30mA until the buck output achieves regulation. The input voltage range is ideally suited for applications powered from a Li-Ion battery and 5V or 3.3V rails.

FEATURES
■ High Efficiency 500mA Buck Plus 300mA VLDO
   Regulator
   Auto Start-Up Powers VLDO/Linear Regulator
   Output Prior to Buck Output
■ Independent 500mA High Efficiency Buck
   (VIN: 2.7V to 5.5V)
■ 300mA VLDO Regulator with 30mA Standalone Mode
■ No External Schottky Diodes Required
■ Fixed Buck Output Voltage: 1.8V
■ VLDO Input Voltage Range (LVIN: 1.675V to 5.5V)
■ Fixed VLDO Output Voltage: 1.575V
■ Selectable Fixed Frequency, Pulse-Skip Operation
   or Burst Mode® Operation
■ Short-Circuit Protected
■ Current Mode Operation for Excellent Line and Load
   Transient Response
■ Shutdown Current: <3µA
■ Constant Frequency Operation: 2.25MHz
■ Low Dropout Buck Operation: 100% Duty Cycle
■ Small, Thermally Enhanced, 10-Lead (3mm × 3mm)
   DFN Package

APPLICATIONS
■ Digital Cameras
■ Cellular Phones
■ PC Cards
■ Wireless and DSL Modems
■ Other Portable Power Systems