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LTC3541 - High Efficiency Buck + VLDO Regulator

The LTC3541 combines a synchronous buck DC/DC converter with a very low dropout linear regulator (VLDO) to provide up to two output voltages from a single input voltage with minimal external components. When configured for dual output operation, the LTC3541’s auto start-up feature will bring the Buck output into regulation in a controlled manner prior to enabling the VLDO regulator output without the need for external pin control. VLDO/ linear regulator output prior to Buck output sequencing may also be obtained via external pin control. The input voltage range is ideally suited for Li-Ion battery-powered applications, as well as powering sub-3.3V logic from 5V or 3.3V rails.

The synchronous buck converter provides a high efficiency output, typically 90%, capable of providing up to 500mA of continuous output current while switching at 2.25MHz, allowing the use of small surface mount inductors and capacitors. A mode-select pin allows Burst Mode operation to be enabled for higher effi ciency at light load currents, or disabled for lower noise, constant frequency operation.

The VLDO regulator provides a low noise, low voltage output capable of providing up to 300mA of continuous output current using only a 2.2μF ceramic capacitor. The input supply voltage of the VLDO regulator (LVIN) may come from the buck regulator or a separate supply.

Features High Efficiency, 500mA Buck Plus 300mA VLDO Regulator Auto Start-Up Powers Buck Output Prior to VLDO/Linear Regulator Output Independent High Efficiency, 500mA Buck (VIN: 2.7V to 5.5V) 300mA VLDO Regulator with 30mA Standalone Mode No External Schottky Diodes Required Buck Output Voltage Range: 0.8V to 5V VLDO Input Voltage Range (LVIN): 0.9V to 5.5V VLDO Output Voltage Range VLDO: 0.4V to 4.1V Selectable Fixed Frequency, Pulse-Skip Operation or Burst Mode® Operation Short-Circuit Protected Current Mode Operation for Excellent Line and Load Transient Response Constant Frequency Operation: 2.25MHz Low Dropout Buck Operation: 100% Duty Cycle Small, Thermally Enhanced, 10-Lead (3mm × 3mm) DFN Package Typical Application

Applications PDAs/Palmtop PCs Digital Cameras Cellular Phones PC Cards Wireless and DSL Modems Other Portable Power Systems Packaging

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