Document
LTC3541-1
High Efficiency Buck + VLDO Regulator
FEATURES
nn High Efficiency, 500mA Buck Plus 300mA VLDO™ Regulator nn Auto Start-Up Powers VLDO/Linear Regulator Output Prior to Buck Regulator Output
nn Independent High Efficiency, 500mA Buck (VIN: 2.7V to 5.5V)
nn 300mA VLDO Regulator with 30mA Standalone Mode nn No External Schottky Diodes Required nn Buck Output Voltage Range: 0.8V to 5V nn VLDO Input Voltage Range (LVIN): 0.9V to 5.5V nn VLDO Output Voltage Range VLDO: 0.4V to 4.1V nn Selectable Fixed Frequency, Pulse-Skip Operation or nn Burst Mode® Operation nn Short-Circuit Protected nn Current Mode Operation for Excellent Line and Load
Transient Response nn Constant Frequency Operation: 2.25MHz nn Low Dropout Buck Operation: 100% Duty Cycle nn Small, Thermally Enhanced, 10-Lead (3mm × 3mm)
DFN Package
APPLICATIONS
nn PDAs/Palmtop PCs nn Digital Cameras nn Cellular Phones nn PC Cards nn Wireless and DSL Modems nn Other Portable Power Systems
DESCRIPTION
The LTC®3541-1 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 LTC3541-1’s auto start-up feature will bring the VLDO/linear regulator output into regulation in a controlled manner prior to enabling the Buck regulator output without the need for external pin control. Buck output prior to VLDO/linear regulator output sequencing may also be obtained via external pin control. The input voltage range is ideally suited for Li-Ion batterypowered 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.
L, LT, LTC, LTM, Linear Technology and the Linear logo are registered trademarks and 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.
TYPICAL APPLICATION
VIN 2.9V TO 5.5V
VOUT1 2.5V
200mA
10µF
LTC3541-1 Typical Application
10µF 2.2µH
VIN
ENBUCK ENVLDO MODE
SW
LVIN
LVOUT
22pF 243k
LTC3541-1
412k
BUCKFB
LFB
115k PGND
GND
150k
VOUT2 1.5V 300mA
2.2µF
35411 TA01a
Buck (Burst) Efficiency and Power Loss vs Load Current
EFFICIENCY (%)
100
1
90 EFFICIENCY
80 0.1
70
60
POWE.