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LTC3547
1
3547fa
OUTPUT CURRENT (mA)
30
EFFICIENCY
(%)
POWER
LOSS
(W)
90
100
20
10
80
50
70
60
40
0.1
10
100
1000
3547 TA01b
0
1
0.1
0.01
0.001
0.0001
1
VIN = 2.7V
VIN = 3.6V
VIN = 4.2V
Dual Monolithic
300mA Synchronous
Step-Down Regulator
The LTC3547 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 and USB powered applications. Supply current dur-
ing operation is only 40A and drops to < 1A in shutdown.
Automatic Burst Mode operation increases efciency at
light loads, further extending battery life.
An internally set 2.25MHz switching frequency allows
the use of tiny surface mount inductors and capacitors.
Internal soft-start reduces inrush current during start-
up. All outputs are internally compensated to work with
ceramic capacitors. The LTC3547 is available in a low
prole (0.75mm) 3mm × 2mm DFN package. The LTC3547
is also available in a xed output voltage conguration,
eliminating the need for the external feedback networks
(see Table 2).
■
Cellular Telephones
■
Digital Still Cameras
■
Wireless and DSL Modems
■
PDAs/Palmtop PCs
■
Portable Media Players
■
High Efciency Dual Step-Down Outputs: Up to 96%
■
300mA Output Current per Channel at VIN = 3V
■
Automatic Low Ripple Burst Mode Operation
(20mVP-P)
■
Only 40A Quiescent Current During Operation
(Both Channels)
■
2.25MHz Constant-Frequency Operation
■
2.5V to 5.5V Input Voltage Range
■
Low Dropout Operation: 100% Duty Cycle
■
Internally Compensated for All Ceramic Capacitors
■
Independent Internal Soft-Start for Each Channel
■
Current Mode Operation for Excellent Line and Load
Transient Response
■
0.6V Reference Allows Low Output Voltages
■
Short-Circuit Protected
■
Ultralow Shutdown Current: IQ < 1A
■
Low Prole (0.75mm) 8-Lead 3mm × 2mm
DFN Package
Dual Monolithic Buck Regulator in 8-Lead 3mm × 2mm DFN
APPLICATIO S
U
FEATURES
DESCRIPTIO
U
TYPICAL APPLICATIO
U
, 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.
VIN
RUN2
RUN1
LTC3547
VFB2
SW2
SW1
VFB1
10pF
GND
VIN
2.5V TO 5.5V
VOUT2
1.8V AT
300mA
VOUT1
2.5V AT
300mA
3547 TA01
237k
150k
475k
L2
4.7
H
L1
4.7
H
475k
4.7
F
4.7
F
4.7
F
Efciency vs Output Current
for VOUT = 2.5V