LTC3547 Datasheet, PDF (1/16 Pages) Linear Technology – Dual Monolithic 300mA Synchronous Step-Down Regulator

FEATURES
■ _{High Efficiency Dual Step-Down Outputs: Up to 96%}
■ _{300mA Output Current per Channel at VIN = 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: IQ < 1µA}
■ _{Low Profile (0.75mm) 8-Lead 3mm × 2mm}
DFN Package
U
APPLICATIO S
■ _{Cellular Telephones}
■ _{Digital Still Cameras}
■ _{Wireless and DSL Modems}
■ _{PDAs/Palmtop PCs}
■ _{Portable Media Players}
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.
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
L2
4.7µH
10pF
RUN2 V_IN RUN1
LTC3547
SW2
SW1
L1
4.7µH
10pF
V_OUT1
2.5V AT
300mA
4.7µF ^475k
V_FB2
V_FB1
GND
237k
150k ^475k
4.7µF
3547 TA01
Efficiency vs Output Current
for V_OUT = 2.5V
100
1
90
80
0.1
70
60
50
0.01
40
30
20
10
0
0.1
0.001
V_IN = 2.7V
V_IN = 3.6V
V_IN = 4.2V
0.0001
1
10
100
1000
OUTPUT CURRENT (mA)
3547 TA01b
3547fa
1