LTC3548A Datasheet, PDF (1/20 Pages) Linear Technology – Dual Synchronous 400mA/800mA, 2.25MHz Step-Down DC/DC Regulator

LTC3548A
Dual Synchronous
400mA/800mA, 2.25MHz
Step-Down DC/DC Regulator
FEATURES
DESCRIPTION
n _{High Efficiency: Up to 95%}
n _{Low Ripple (<35mVP-P) Burst Mode Operation;}
I_Q = 40μA
n _{2.25MHz Constant Frequency Operation}
n _{High Switch Current: 0.7A and 1.2A}
n _{No Schottky Diodes Required}
n _{Low RDS(ON) Internal Switches: 0.35Ω}
n _{Current Mode Operation for Excellent Line}
and Load Transient Response
n _{Short-Circuit Protected}
n _{Low Dropout Operation: 100% Duty Cycle}
n _{Ultralow Shutdown Current: IQ <1μA}
n _{Output Voltages from 5V down to 0.6V}
n _{Power-On Reset Output}
n _{Externally Synchronizable Oscillator}
n _{Optional External Soft-Start}
n _{Small Thermally Enhanced MSOP and 3mm × 3mm}
DFN Packages
APPLICATIONS
n _{PDAs/Palmtop PCs}
n _{Digital Cameras}
n _{Cellular Phones}
n _{Wireless and DSL Modems}
The LTC^®3548A is a dual, constant frequency, synchronous
step-down DC/DC converter. Intended for low power ap-
plications, 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, 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 ripple noise for low power efficiency. Burst
Mode^® operation provides the highest efficiency at light
loads, while pulse-skipping 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.
L, LT, LTC, LTM, Linear Technology, the Linear logo 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.
TYPICAL APPLICATION
2.5V/1.8V at 400mA/800mA Step-Down Regulators
V_IN
2.5V TO 5.5V
10μF
V_OUT2
2.5V
400mA
4.7μH
22pF
RUN/SS2 V_IN RUN/SS1
MODE/SYNC
POR
SW2
SW1
LTC3548A
100k
RESET
2.2μH
22pF
V_OUT1
1.8V
800mA
V_FB2
V_FB1
887k
4.7μF
280k
GND
442k ^887k
10μF
3548A TA01
Efficiency/Power Loss Curves
100
2.5V
90
80
70
60
1
1.8V
0.1
50
0.01
40
30
20
10
0
1
0.001
V_IN = 3.3V
Burst Mode OPERATION
NO LOAD ON OTHER CHANNEL
0.0001
10
100
1000
LOAD CURRENT (mA)
3548A TA02
3548af
1