LTC3541 High Efficiency Buck + VLDO Regulator FEATURESDESCRIPTION n High Efficiency, 500mA Buck Plus 300mA VLDO™ The LTC®3541 combines a synchronous buck DC/ Regulator DC converter with a very low dropout linear regulator n Auto Start-Up Powers Buck Output Prior (VLDO) to provide up to two output voltages from a single to VLDO/Linear Regulator Output input voltage with minimal external components. When n Independent High Efficiency, 500mA Buck configured for dual output operation, the LTC3541’s auto (VIN: 2.7V to 5.5V) start-up feature will bring the Buck output into regulation n 300mA VLDO Regulator with 30mA Standalone Mode in a controlled manner prior to enabling the VLDO regulator n No External Schottky Diodes Required output without the need for external pin control. VLDO/ n Buck Output Voltage Range: 0.8V to 5V linear regulator output prior to Buck output sequencing n VLDO Input Voltage Range (LVIN): 0.9V to 5.5V may also be obtained via external pin control. The input n VLDO Output Voltage Range VLDO: 0.4V to 4.1V voltage range is ideally suited for Li-Ion battery-powered n Selectable Fixed Frequency, Pulse-Skip Operation or applications, as well as powering sub-3.3V logic from 5V n Burst Mode® Operation or 3.3V rails. n Short-Circuit Protected The synchronous buck converter provides a high efficiency n Current Mode Operation for Excellent Line and Load output, typically 90%, capable of providing up to 500mA Transient Response of continuous output current while switching at 2.25MHz, n Constant Frequency Operation: 2.25MHz allowing the use of small surface mount inductors and ca- n Low Dropout Buck Operation: 100% Duty Cycle pacitors. A mode-select pin allows Burst Mode operation n Small, Thermally Enhanced, 10-Lead (3mm × 3mm) to be enabled for higher efficiency at light load currents, or DFN Package disabled for lower noise, constant frequency operation. APPLICATIONS The VLDO regulator provides a low noise, low voltage output capable of providing up to 300mA of continuous n PDAs/Palmtop PCs output current using only a 2.2µF ceramic capacitor. The n Digital Cameras input supply voltage of the VLDO regulator (LV n Cellular Phones IN) may come from the buck regulator or a separate supply. n PC Cards L, LT, LTC, LTM, Linear Technology and the Linear logo are registered trademarks and VLDO is a n Wireless and DSL Modems trademark of Linear Technology Corporation. All other trademarks are the property of their respective n Other Portable Power Systems owners. Protected by U.S. Patents, including 5481178, 6611131, 6304066, 6498466, 6580258. TYPICAL APPLICATIONBuck (Burst) Efficiency and Power Loss vs Load CurrentLTC3541 Typical Application 100 1 V 90 IN EFFICIENCY 2.9V TO 5.5V 10µF 80 V 0.1 IN POWER LOSS (W) 70 ENVLDO ENBUCK 2.2µH V 60 OUT2 POWER LOSS SW LVOUT 1.5V V 50 0.01 OUT1 2.5V LV 300mA IN 412k LTC3541 40 200mA EFFICIENCY (%) 22pF 243k LFB 30 0.001 10µF 2.2µF BUCKFB MODE 20 115k 10 V PGND GND 150k IN = 3.3V VOUT = 2.5V 0 0.0001 1 10 100 1000 3541 TA01a LOAD CURRENT (mA) 3541 TA01b 3541fb For more information www.linear.com/LTC3541 1 For more information www.linear.com/LTC3541 Document Outline Features Applications Typical Application Description Absolute Maximum Ratings Order Information Pin Configuration Electrical Characteristics Typical Performance Characteristics Pin Functions Block Diagram Operation Applications Information BUCK Regulator VLDO/Linear regulator Applications Information Efficiency Considerations Thermal Considerations Applications Information Pc Board Layout Checklist Design Example Typical Applications Package Description Revision History Related Parts
