Internal Switches: 0.35鈩?/div>
Current Mode Operation for Excellent Line
and Load Transient Response
Short-Circuit Protected
Low Dropout Operation: 100% Duty Cycle
Ultralow Shutdown Current: I
Q
< 1碌A
Output Voltages from 5V down to 0.6V
Power-On Reset Output
Externally Synchronizable Oscillator
Small Thermally Enhanced MSOP and 3mm
脳
3mm
DFN Packages
The LTC
廬
3548 is a dual, constant frequency, synchronous
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
鈮?.2mm.
Each output voltage is adjustable
from 0.6V to 5V. Internal synchronous 0.35鈩? 0.7A/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
廬
operation provides high efficiency at light loads,
while Pulse Skip Mode provides low noise ripple at light
loads.
To further maximize battery runtime, the P-channel
MOSFETs are turned on continuously in dropout (100%
duty cycle), and both channels draw a total quiescent
current of only 40碌A. In shutdown, the device draws <1碌A.
, LTC and LT are registered trademarks of Linear Technology Corporation. All other
trademarks are the property of their respective owners. Burst Mode is a registered
trademark of Linear Technology Corporation. Protected by U.S. Patents including 5481178,
6580258, 6304066, 6127815, 6498466, 6611131.
APPLICATIO S
鈻?/div>
鈻?/div>
鈻?/div>
鈻?/div>
鈻?/div>
鈻?/div>
PDAs/Palmtop PCs
Digital Cameras
Cellular Phones
Portable Media Players
PC Cards
Wireless and DSL Modems
TYPICAL APPLICATIO
V
IN
= 2.8V
TO 5.5V
10碌F
RUN2
V
IN
RUN1
POR
100k
RESET
MODE/SYNC
LTC3548
V
OUT2
= 2.5V
AT 400mA
4.7碌H
SW2
68pF
EFFICIENCY (%)
2.2碌H
SW1
33pF
V
OUT1
= 1.8V
AT 800mA
887k
4.7碌F
280k
V
FB2
GND
V
FB1
604k
301k
10碌F
3548 TA01
Figure 1. 2.5V/1.8V at 400mA/800mA Step-Down Regulators
U
LTC3548 Efficiency Curve
100
95
90
85
80
POWER LOSS
75
70
65
60
1
V
IN
= 3.3V, V
OUT
= 1.8V
Burst Mode OPERATION
CHANNEL 1, NO LOAD ON CHANNEL 2
10
100
LOAD CURRENT (mA)
1
10
EFFICIENCY
100
POWER LOSS (mW)
1000
0.1
1000
3548 TA02
U
U
3548f
1
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