LTC3548EDD Datasheet, PDF (1/16 Pages) Linear Technology – Dual Synchronous, 400mA/800mA, 2.25MHz

LTC3548
Dual Synchronous,
400mA/800mA, 2.25MHz
Step-Down DC/DC Regulator
FEATURES
n _{High Efficiency: Up to 95%}
n _{Very Low Quiescent Current: Only 40μA}
n _{Low Output Ripple Burst Mode}^® _Operation
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 _{Small Thermally Enhanced MSOP and 3mm × 3mm}
DFN Packages
APPLICATIONS
■ _{PDAs/Palmtop PCs}
■ _{Digital Cameras}
■ _{Cellular Phones}
■ _{Portable Media Players}
■ _{PC Cards}
■ _{Wireless and DSL Modems}
DESCRIPTION
The LTC^®3548 is a dual, constant-frequency, synchronous
step down DC/DC converter. Intended for low power ap-
plications, 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 ≤1mm. 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 noise ripple for low power efficiency. Burst
Mode operation provides high efficiency at light loads,
while pulse-skipping 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 cur-
rent 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, 6127815, 6304066, 6498466, 6580258
6611131..
TYPICAL APPLICATION
V_IN = 2.8V
TO 5.5V
V_OUT2 = 2.5V
AT 400mA
10μF
4.7μH
68pF
RUN2 V_IN RUN1
MODE/SYNC
POR
LTC3548
SW2
SW1
100k
RESET
2.2μH
33pF
V_OUT1 = 1.8V
AT 800mA
V_FB2
887k
V_FB1
4.7μF
280k
GND
604k
301k
10μF
3548 TA01
Figure 1. 2.5V/1.8V at 400mA/800mA Step-Down Regulators
LTC3548 Efficiency Curve
100
1000
95
90
EFFICIENCY
100
85
80
10
POWER LOSS
75
70
65
60
1
1
V_IN = 3.3V, V_OUT = 1.8V
Burst Mode OPERATION
CHANNEL 1, NO LOAD ON CHANNEL 2 _0.1
10
100
1000
LOAD CURRENT (mA)
3548 TA02
3548fc
1