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LTC3541-3 - High Efficiency Buck + VLDO Regulator

The LTC3541-3 combines a synchronous buck DC/ DC converter with a very low dropout linear regulator (VLDOTM regulator) 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 feature will bring the 1.575V VLDO/linear regulator output into regulation in a controlled manner prior to enabling the 1.8V buck output without 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.

The synchronous buck converter provides a high efficiency output, typically 90%. It can provide up to 500mA of 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 efficiency 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 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 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 Typical Application

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

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