Datasheet
LTC3407A-2
1
3407a2f
■
High Efficiency: Up to 95%
■
Low Ripple (<35mV
PK-PK
) Burst Mode Operation;
I
Q
= 40μA
■
2.25MHz Constant Frequency Operation
■
No Schottky Diodes Required
■
Low R
DS(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: I
Q
<1μA
■
Output Voltages from 5V down to 0.6V
■
Power-On Reset Output
■
Externally Synchronizable Oscillator
■
Optional External Soft-Start
■
Small Thermally Enhanced MSOP and 3mm × 3mm
DFN Packages
APPLICATIO S
U
FEATURES
TYPICAL APPLICATIO
U
DESCRIPTIO
U
■
PDAs/Palmtop PCs
■
Digital Cameras
■
Cellular Phones
■
Wireless and DSL Modems
Dual Synchronous 800mA,
2.25MHz Step-Down
DC/DC Regulator
The LTC
®
3407A-2 is a dual, constant frequency, synchro-
nous step-down DC/DC converter. Intended for low power
applications, it operates from a 2.5V to 5.5V input voltage
range and has a constant 2.25MHz switching frequency,
enabling the use of tiny, low cost capacitors and inductors
1mm or less in height. Each output voltage is adjustable
from 0.6V to 5V. Internal synchronous 0.35Ω, 1A 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 ripple noise for low power efficiency. Burst
Mode
®
operation provides the highest efficiency at light
loads, while Pulse Skip Mode provides the lowest ripple
noise 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
40μA. In shutdown, the device draws <1μA.
Efficiency/Power Loss Curve
1mm High 2.5V/1.8V at 800mA Step-Down Regulators
RUN/SS2 V
IN
V
IN
= 2.5V
TO 5.5V
V
OUT2
= 2.5V
AT 800mA
V
OUT1
= 1.8V
AT 800mA
RUN/SS1
POR
SW1
V
FB1
GND
V
FB2
SW2
MODE/SYNC
LTC3407A-2
10μF
100k
RESET
22pF22pF
2.2μH2.2μH
887k 887k
442k280k
10μF
10μF
3407A2 TA01
, LT, LTC, LTM and Burst Mode are registered trademarks of Linear Technology
Corporation. All other trademarks are the property of their respective owners. Protected by
U.S. Patents including 5481178, 6580258, 6304066, 6127815, 6498466, 6611131.
LOAD CURRENT (mA)
1
0
EFFICIENCY (%)
POWER LOSS (W)
30
20
10
70
60
50
40
100
0.0001
0.001
0.1
0.01
1
90
80
10 100 1000
3407A2 TA02
2.5V
V
IN
= 3.3V
Burst Mode OPERATION
NO LOAD ON OTHER CHANNEL
1.8V