LTC3403
1.5MHz, 600mA
Synchronous Step-Down
Regulator with Bypass Transistor
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FEATURES
DESCRIPTIO
The LTC®3403 is a high efficiency monolithic synchro-
nous buck regulator optimized for WCDMA power ampli-
fier applications. The output voltage can be dynamically
programmed from 0.3V to 3.5V. At VOUT > 3.6V an internal
bypass P-channel MOSFET connects VOUT directly to VIN,
eliminating power loss through the inductor. Selectable
forcedcontinuousmodeenablesfastVOUT responsetothe
controlling input.
Supply current is only 20µA in Burst Mode® operation and
drops to <1µA in shutdown. The 2.5V to 5V input voltage
range makes the LTC3403 ideally suited for single Li-Ion
battery-powered applications. 100% duty cycle provides
low dropout operation, extending battery life in portable
systems.
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Dynamically Adjustable Output from 0.3V to 3.5V
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Very Low Quiescent Current: Only 20
µA
During Operation
600mA Output Current
Internal P-Channel MOSFET Bypass Transistor
High Efficiency: Up to 96%
1.5MHz Constant Frequency Operation
No Schottky Diode Required
Low Dropout Operation: 100% Duty Cycle
2.5V to 5V Input Voltage Range
Drives Optional External P-Channel MOSFET
Shutdown Mode Draws <1µA Supply Current
Current Mode Operation for Excellent Line and
Load Transient Response
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Overtemperature Protected
Available in 8-Lead 3mm × 3mm DFN Package
Switching frequency is internally set at 1.5MHz, allowing
the use of small surface mount inductors and capacitors.
The internal synchronous switch increases efficiency and
eliminates the need for an external Schottky diode.
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APPLICATIO S
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WCDMA Cell Phone Power Amplifiers
Wireless Modems
The LTC3403 is available in a low profile 8-lead 3mm ×
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3mm DFN package.
, LTC and LT are registered trademarks of Linear Technology Corporation.
Burst Mode is a registered trademark of Linear Technology Corporation.
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TYPICAL APPLICATIO
95
90
V
= 3.6V
IN
85
80
75
70
65
60
55
50
2.2µH*
V
= 4.2V
V
V
IN
IN
2.7V
OUT
3× V
V
SW
LTC3403
MODE GDR
REF
600mA
IN
†
V
= 3.6V
V
= 4.2V
IN
C
**
IN
C
TO 5V
OUT
IN
4.7µF
10µF
CER
CER
V
OUT
RUN
REF
FORCED
CONTINUOUS
MODE
Burst Mode
OPERATION
OUT
GND
OUTPUT
WCDMA
RF PA
PROGRAMMING
DAC
3
V
= 1.8V
*MURATA LQH32CN2R2M11
3403 F01a
0.1
1
10
100
1000
**TAIYO YUDEN JMK212BJ475MG
†
TAIYO YUDEN JMK212BJ106MN
OUTPUT CURRENT (mA)
3403 F01b
Figure 1a. WCDMA Transmitter Power Supply
Figure 1b. Efficiency vs Output Current
3403f
1