Datasheet LTC3547B (Analog Devices)

LTC3547B Dual Monolithic 300mA Synchronous Step-Down Regulator
U FEATURES DESCRIPTIO
■
High Effi ciency (Up to 96%) Dual Step-Down
The LTC®3547B is a dual, 2.25MHz, constant-frequency,
Outputs
synchronous step-down DC/DC converter in a tiny 3mm × ■
300mA Output Current per Channel at VIN = 3V
2mm DFN package. 100% duty cycle provides low drop- ■
2.25MHz Constant-Frequency Operation
out operation, extending battery life in portable systems. ■
2.5V to 5.5V Input Voltage Range
Low output voltages are supported with the 0.6V feed- ■
Low Dropout Operation: 100% Duty Cycle
back reference voltage. Each regulator can supply 300mA ■
No Schottky Diodes Required
continuous output current. ■
Internally Compensated for All Ceramic Capacitors
The input voltage range is 2.5V to 5.5V, making it ideal ■
Independent Internal Soft-Start for Each Channel
for Li-Ion polymer and USB powered applications. Supply ■ Available in Fixed Output Versions current is only 1μA in shutdown. ■ Current Mode Operation for Excellent Line and Load Transient Response An internally set 2.25MHz switching frequency allows the ■ 0.6V Reference Allows Low Output Voltages use of tiny surface mount inductors and capacitors. Inter- ■ Short-Circuit Protected nal soft-start reduces inrush current during start-up. All ■ Ultralow Shutdown Current: I outputs are internally compensated to work with ceramic Q < 1μA ■ Low Profi le (0.75mm) 8-Lead 3mm × 2mm capacitors. The LTC3547B is available in a low profi le DFN Package (0.75mm) 3mm × 2mm DFN package. The LTC3547B is also available in a fi xed output voltage confi guration
U
selected via internal resistor dividers (see Table 2).
APPLICATIO S
, LT, LTC and LTM are registered trademarks of Linear Technology Corporation. Burst Mode is a registered trademark of Linear Technology Corporation. All other ■ Cellular Telephones trademarks are the property of their respective owners. Protected by U.S. Patents, ■ Digital Still Cameras including 6580258, 5481178, 6304066, 6127815, 6498466, 6611131. ■ Wireless and DSL Modems ■ Portable Media Players ■ PDAs/Palmtop PCs
U TYPICAL APPLICATIO Effi ciency vs Output Current for VOUT = 2.5V
100 1
Dual Monolithic Buck Regulator in 8-Lead 3mm × 2mm DFN
90 VIN 80 2.5V TO 5.5V POWER LOSS (W) 4.7μF 70 0.1 RUN2 VIN RUN1 60 LTC3547B 50 V 4.7μH 4.7μH OUT2 VOUT1 1.8V AT SW2 SW1 2.5V AT 40 300mA 10pF 10pF 300mA EFFICIENCY (%) 0.01 30 20 V V IN = 2.7V VFB2 FB1 475k GND 10 VIN = 3.6V 475k 4.7μF 237k 150k 4.7μF VIN = 4.2V 0 0.001 1 10 100 1000 3547b TA01 OUTPUT CURRENT (mA) 3547b TA01b 3547bfb 1