FEATURES
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LTC3547
Dual Monolithic
300mA Synchronous
Step-Down Regulator
DESCRIPTIO
The LTC
®
3547 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 40µA and drops to < 1µA in shutdown.
Automatic Burst Mode
®
operation increases efficiency 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
profile (0.75mm) 3mm
×
2mm DFN package. The LTC3547
is also available in a fixed output voltage configuration,
eliminating the need for the external feedback networks
(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.
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High Efficiency Dual Step-Down Outputs: Up to 96%
300mA Output Current per Channel at V
IN
= 3V
Automatic Low Ripple Burst Mode Operation
(20mV
P-P
)
Only 40µA 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: I
Q
< 1µA
Low Profile (0.75mm) 8-Lead 3mm
×
2mm
DFN Package
APPLICATIO S
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Cellular Telephones
Digital Still Cameras
Wireless and DSL Modems
PDAs/Palmtop PCs
Portable Media Players
TYPICAL APPLICATIO
V
IN
2.5V TO 5.5V
Dual Monolithic Buck Regulator in 8-Lead 3mm × 2mm DFN
100
90
80
RUN2 V
IN
RUN1
V
OUT2
1.8V AT
300mA
L2
4.7µH
10pF
LTC3547
SW2
SW1
10pF
L1
4.7µH
V
OUT1
2.5V AT
300mA
EFFICIENCY (%)
4.7µF
70
60
50
40
30
20
V
FB2
V
IN
= 2.7V
V
IN
= 3.6V
V
IN
= 4.2V
1
10
100
OUTPUT CURRENT (mA)
4.7µF
475k
237k
GND
V
FB1
150k
475k
4.7µF
3547 TA01
10
0
0.1
U
U
U
Efficiency vs Output Current
for V
OUT
= 2.5V
1
0.1
POWER LOSS (W)
0.01
0.001
0.0001
1000
3547fa
3547 TA01b
1
LINEAR [ LINEAR INTEGRATED SYSTEMS ]
