LTC3548 Datasheet, PDF (1/16 Pages) Linear Technology – Dual Synchronous, 400mA/800mA, 2.25MHz Step-Down DC/DC Regulator

LTC3548
Dual Synchronous,
400mA/800mA, 2.25MHz
Step-Down DC/DC Regulator
FEATURES
■ _{High Efficiency: Up to 95%}
■ _{Very Low Quiescent Current: Only 40µA}
■ _{2.25MHz Constant Frequency Operation}
■ _{High Switch Current: 0.7A and 1.2A}
■ _{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
U
APPLICATIO S
■ _{PDAs/Palmtop PCs}
■ _{Digital Cameras}
■ _{Cellular Phones}
■ _{Portable Media Players}
■ _{PC Cards}
■ _{Wireless and DSL Modems}
DESCRIPTIO
The LTC^®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 ≤1.2mm. 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 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 40µA. In shutdown, the device draws <1µA.
, 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.
TYPICAL APPLICATIO
V_IN = 2.8V
TO 5.5V
10µF
V_OUT2 = 2.5V
AT 400mA
4.7µH
68pF
RUN2 V_IN RUN1
MODE/SYNC
POR
LTC3548
SW2
SW1
100k
RESET
2.2µH
33pF
V_OUT1 = 1.8V
AT 800mA
4.7µF
887k
280k
V_FB2
GND
V_FB1
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
3548f
1