LTC3408_15 Datasheet, PDF (1/12 Pages) Linear Technology – 1.5MHz, 600mA Synchronous Step-Down Regulator with Bypass Transistor

LTC3408
1.5MHz, 600mA
Synchronous Step-Down
Regulator with Bypass Transistor
FEATURES
■ _{Dynamically Adjustable Output from 0.3V to 3.5V}
■ _{600mA Output Current}
■ _{Internal 0.08Ω 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}
■ _{Shutdown Mode Draws < 1µA Supply Current}
■ _{Current Mode Operation for Excellent Line and}
Load Transient Response
■ _{Overtemperature Protected}
■ _{Available in 8-Lead 3mm × 3mm DFN Package}
U
APPLICATIO S
■ _{WCDMA Cell Phone Power Amplifiers}
■ _{Wireless Modems}
DESCRIPTIO
The LTC^®3408 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 V_OUT > 3.6V an internal
0.08Ω bypass P-channel MOSFET connects V_OUT directly
to V_IN, eliminating power loss through the inductor.
The input voltage range is 2.5V to 5V making the LTC3408
ideally suited for single Li-Ion battery-powered applica-
tions. 100% duty cycle provides low dropout operation,
extending battery life in portable systems.
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.
The LTC3408 is available in a low profile (0.75mm) 8-lead
3mm × 3mm DFN package.
, LTC and LT are registered trademarks of Linear Technology Corporation.
U.S. Patent Numbers: 5481178, 6580258, 6304066, 6127815, 6498466, 6611131
TYPICAL APPLICATIO
WCDMA Transmitter Power Supply
V_IN
2.7V
TO 5V
OUTPUT
PROGRAMMING
DAC
C_IN†
10µF
CER
V_IN
SW
LTC3408
RUN V_OUT
REF
GND
4.7µH*
*MURATA LQH32CN4R7M11
**TAIYO YUDEN JMK212BJ475MG
†_{TAIYO YUDEN JMK212BJ106MN}
C_OUT**
4.7µF
CER
V_OUT
3× V_REF
600mA
WCDMA
RF PA
3403 TA01
Efficiency Power Lost vs Load Current
1
100
90
80
70
0.1
60
50
0.01
0.01
1
40
30
V_OUT = 1.2V
V_OUT = 1.5V
20
V_OUT = 1.8V ₁₀
V_OUT = 2.5V
0
10
100
1000
LOAD CURRENT (mA)
3408 F04
3408f
1