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LTC3407-2
1
34072fa
APPLICATIO S
U
FEATURES
TYPICAL APPLICATIO
U
DESCRIPTIO
U
■ PDAs/Palmtop PCs
■ Digital Cameras
■ Cellular Phones
■ Portable Media Players
■ PC Cards
■ Wireless and DSL Modems
■ High Efficiency: Up to 95%
■ Very Low Quiescent Current: Only 40
μA
■ 2.25MHz Constant Frequency Operation
■ High Switch Current: 1.2A on Each Channel
■ No Schottky Diodes Required
■ Low RDS(ON) Internal Switches: 0.35Ω
■ Current Mode Operation for Excellent Line
and Load Transient Response
■ Short-Circuit Protected
■ Low Dropout Operation: 100% Duty Cycle
■ Ultralow Shutdown Current: IQ < 1μA
■ Output Voltages from 5V down to 0.6V
■ Power-On Reset Output
■ Externally Synchronizable Oscillator
■ Small Thermally Enhanced MSOP and 3mm
× 3mm
DFN Packages
Dual Synchronous, 800mA,
2.25MHz Step-Down
DC/DC Regulator
The LTC
3407-2 is a dual, constant frequency, synchro-
nous step down DC/DC converter. Intended for low power
applications, it operates from 2.5V to 5.5V input voltage
range and has a constant 2.25MHz switching frequency,
allowing the use of tiny, low cost capacitors and inductors
with a profile
≤1.2mm. Each output voltage is adjustable
from 0.6V to 5V. Internal synchronous 0.35
Ω, 1.2A power
switches provide high efficiency without the need for
external Schottky diodes.
A user selectable mode input is provided to allow the user
to trade-off noise ripple for low power efficiency. Burst
Mode
operation provides high efficiency at light loads,
while Pulse Skip Mode provides low noise ripple at light
loads.
To further maximize battery life, the P-channel MOSFETs
are turned on continuously in dropout (100% duty cycle),
and both channels draw a total quiescent current of only
40
μA. In shutdown, the device draws <1μA.
LTC3407-2 Efficiency Curve
Figure 1. 2.5V/1.8V at 800mA Step-Down Regulators
RUN2
VIN
VIN = 2.5V*
TO 5.5V
VOUT2 = 2.5V
AT 800mA
VOUT1 = 1.8V
AT 800mA
RUN1
POR
SW1
VFB1
GND
VFB2
SW2
MODE/SYNC
LTC3407-2
C1
10
μF
R5
100k
RESET
C4, 22pF
C5, 22pF
L1
2.2
μH
L2
2.2
μH
R4
887k
R2
604k
R1
301k
R3
280k
C3
10
μF
C2
10
μF
3407 TA01
C1, C2, C3: TAIYO YUDEN JMK316BJ106ML
L1, L2: MURATA LQH32CN2R2M33
*VOUT CONNECTED TO VIN FOR VIN ≤ 2.8V
LOAD CURRENT (mA)
1
EFFICIENCY
(%)
100
95
90
85
80
75
70
65
60
10
100
1000
3407 TA02
VIN = 3.3V
Burst Mode OPERATION
NO LOAD ON OTHER CHANNEL
2.5V
1.8V
, LT, LTC, LTM, and Burst Mode are registered trademarks of Linear Technology
Corporation. All other trademarks are the property of their respective owners.