LTC3541_15 Datasheet, PDF (1/20 Pages) Linear Technology – High Efficiency Buck VLDO Regulator

LTC3541
High Efficiency
Buck + VLDO Regulator
FEATURES
DESCRIPTIO
■ _{High Efficiency, 500mA Buck Plus 300mA VLDO}^TM
Regulator
Auto Start-Up Powers Buck Output Prior to
VLDO/Linear Regulator Output
■ _{Independent High Efficiency, 500mA Buck}
(V_IN: 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 _U
APPLICATIO S
■ _{PDAs/Palmtop PCs}
■ _{Digital Cameras}
■ _{Cellular Phones}
■ _{PC Cards}
■ _{Wireless and DSL Modems}
■ _{Other Portable Power Systems}
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 ca-
pacitors. 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 (LV_IN) 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
TYPICAL APPLICATIO
LTC3541 Typical Application
V_IN
2.9V TO 5.5V
SW ENVLDO
V_OUT1
2.5V
200mA
2.2µH
243k
22pF
10µF
V_IN
MODE
LTC3541
ENBUCK GND
BUCKFB LFB
LV_IN
LV_OUT
PGND
115k
150k
412k
V_OUT2
1.5V
300mA
2.2µF
3541 TA01a
Buck (Burst) Efficiency and Power Loss vs Load Current
100
1
90
EFFICIENCY
80
0.1
70
60
POWER LOSS
50
0.01
40
30
20
10 VIN = 3.3V
0 ^{VOUT = 2.5V}
1
10
100
LOAD CURRENT (mA)
0.001
0.0001
1000
3541 TA01b
3541fa