LTC3541

LTC3541 High Efficiency Buck + VLDO Regulator High Efficiency, 500mA Buck Plus 300mA VLDOTM 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 (LV ): 0.9V to 5.5V IN ■ 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 ■ The LTC ®3541 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 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 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. , LT, LTc and LTM are registered trademarks of Linear Technology corporation. VLDO is a trademark of Linear Technology corporation. All other trademarks are the property of their respective owners. Protected by U.S. Patents, including 5481178, 6611131, 6304066, 6498466, 6580258 APPLICATIO S ■ ■ ■ ■ ■ ■ PDAs/Palmtop PCs Digital Cameras Cellular Phones PC Cards Wireless and DSL Modems Other Portable Power Systems LTC3541 Typical Application VIN 2.9V TO 5.5V EFFICIENCY (%) SW 2.2µH 243k VOUT1 2.5V 200mA 22pF VIN ENVLDO 150k MODE LTC3541 ENBUCK GND BUCKFB LVIN LFB LVOUT PGND 10µF 115k U TYPICAL APPLICATIO Buck (Burst) Efficiency and Power Loss vs Load Current 100 90 80 70 60 50 40 30 20 VOUT2 1.5V 300mA 412k 10 0 1 VIN = 3.3V VOUT = 2.5V 10 100 LOAD CURRENT (mA) 2.2µF 3541 TA01a U 1 EFFICIENCY 0.1 POWER LOSS (W) POWER LOSS 0.01 0.001 0.0001 1000 3541 TA01b FEATURES DESCRIPTIO U 3541fa  LTC3541 (Note 1) Supply Voltages: VIN, LVIN .................................................. –0.3V to 6V LVIN – VIN ..........................................................