LTC3547B_15 Datasheet, PDF (1/16 Pages) Linear Technology – Dual Monolithic 300mA Synchronous Step-Down Regulator

FEATURES
■ _{High Efficiency (Up to 96%) Dual Step-Down}
Outputs
■ _{300mA Output Current per Channel at VIN = 3V}
■ _{2.25MHz Constant-Frequency Operation}
■ _{2.5V to 5.5V Input Voltage Range}
■ _{Low Dropout Operation: 100% Duty Cycle}
■ _{No Schottky Diodes Required}
■ _{Internally Compensated for All Ceramic Capacitors}
■ _{Independent Internal Soft-Start for Each Channel}
■ _{Available in Fixed Output Versions}
■ _{Current Mode Operation for Excellent Line and Load}
Transient Response
■ _{0.6V Reference Allows Low Output Voltages}
■ _{Short-Circuit Protected}
■ _{Ultralow Shutdown Current: IQ < 1μA}
■ _{Low Profile (0.75mm) 8-Lead 3mm × 2mm}
DFN Package
U
APPLICATIO S
■ _{Cellular Telephones}
■ _{Digital Still Cameras}
■ _{Wireless and DSL Modems}
■ _{Portable Media Players}
■ _{PDAs/Palmtop PCs}
LTC3547B
Dual Monolithic
300mA Synchronous
Step-Down Regulator
DESCRIPTIO
The LTC^®3547B is a dual, 2.25MHz, constant-frequency,
synchronous step-down DC/DC converter in a tiny 3mm ×
2mm DFN package. 100% duty cycle provides low drop-
out operation, extending battery life in portable systems.
Low output voltages are supported with the 0.6V feed-
back reference voltage. Each regulator can supply 300mA
continuous output current.
The input voltage range is 2.5V to 5.5V, making it ideal
for Li-Ion polymer and USB powered applications. Supply
current is only 1μA in shutdown.
An internally set 2.25MHz switching frequency allows the
use of tiny surface mount inductors and capacitors. Inter-
nal soft-start reduces inrush current during start-up. All
outputs are internally compensated to work with ceramic
capacitors. The LTC3547B is available in a low profile
(0.75mm) 3mm × 2mm DFN package. The LTC3547B
is also available in a fixed output voltage configuration
selected via internal resistor dividers (see Table 2).
, LT, LTC and LTM are registered trademarks of Linear Technology Corporation.
Burst Mode is a registered trademark of Linear Technology Corporation. All other
trademarks are the property of their respective owners. Protected by U.S. Patents,
including 6580258, 5481178, 6304066, 6127815, 6498466, 6611131.
TYPICAL APPLICATIO
Dual Monolithic Buck Regulator in 8-Lead 3mm × 2mm DFN
V_IN
2.5V TO 5.5V
V_OUT2
1.8V AT
300mA
4.7μF
4.7μH
10pF
RUN2 V_IN RUN1
LTC3547B
SW2
SW1
4.7μH
10pF
V_OUT1
2.5V AT
300mA
4.7μF ^475k
V_FB2
V_FB1
GND
237k
150k ^475k
4.7μF
3547b TA01
100
90
80
70
60
50
40
30
20
10
0
1
Efficiency vs Output Current
for V_OUT = 2.5V
1
0.1
0.01
V_IN = 2.7V
V_IN = 3.6V
V_IN = 4.2V
0.001
10
100
1000
OUTPUT CURRENT (mA)
3547b TA01b
3547bfb
1