LTC3521
Wide V , 1A Buck-Boost
IN
DC/DC and Dual 600mA
Buck DC/DC Converters
FeaTures
DescripTion
TheLTC®3521combinesa1Abuck-boostDC/DCconverter
anddual600mAsynchronousbuckDC/DCconverters.The
1.1MHz switching frequency minimizes the solution foot-
printwhilemaintaininghighefficiency.Allthreeconverters
feature soft-start and internal compensation to minimize
the solution footprint and simplify the design process.
n
Three High Efficiency DC/DC Converters:
Buck-Boost (V : 1.8V to 5.25V, I : 1A)
OUT
OUT
Dual Buck (V : 0.6V to V , I : 600mA)
OUT
IN OUT
n
n
n
1.8V to 5.5V Input Voltage Range
Pin-Selectable Burst Mode® Operation
30µA Total Quiescent Current in Burst Mode
Operation
The buck converters are current mode controlled and
utilize an internal synchronous rectifier to improve ef-
ficiency. The buck converters support 100% duty cycle
operation to extend battery life. If the PWM pin is held
low, the buck converters automatically transition from
Burst Mode operation to PWM mode at high loads. With
the PWM pin held high, the buck converters remain in low
noise, 1.1MHz PWM mode.
n
n
n
n
n
Independent Power Good Indicator Outputs
Integrated Soft-Start
Thermal and Overcurrent Protection
<2µA Current in Shutdown
Small 4mm × 4mm QFN and Thermally Enhanced
TSSOP Packages
applicaTions
Thebuck-boostconverterfeaturescontinuousconduction
operation to maximize efficiency and minimize noise. At
light loads, the buck-boost converter can be operated in
Burst Mode operation to improve efficiency and reduce
no-load standby current.
n
Bar Code Readers
n
Medical Instruments
n
Handy Terminals
n
PDAs, Handheld PCs
n
GPS Receivers
The LTC3521 provides a <2μA shutdown mode, over-
temperature shutdown and current limit protection
on all converters. The LTC3521 is available in a 24-pin
0.75mm × 4mm × 4mm QFN package, and a 20-pin
thermally enhanced TSSOP package.
L, LT, LTC, LTM, Linear Technology, Burst Mode and the Linear logo are registered trademarks
and PowerPath is a trademark of Linear Technology Corporation. All other trademarks are the
property of their respective owners. Protected by U. S. Patents, including 6404251, 6166527.
Typical applicaTion
Efficiency vs VIN
V
IN
100
98
+
2.4V TO 4.2V
4.7µF
Li-Ion
4.7µH
4.7µH
4.7µH
V
I
= 3.3V
PV
SW1A
PV
V
OUT1
= 500mA
IN1
IN2
SW2
OUT2
96
94
92
90
88
86
84
82
80
78
76
74
72
70
1.8V
OUT
600mA
137k
10µF
10µF
SW1B
V
OUT1
3.3V
FB2
V
I
= 1.2V
V
OUT1
V
I
= 1.8V
OUT3
= 200mA
OUT2
= 200mA
800mA
(1A, V > 3.0V)
68.1k
OUT
OUT
22µF
1.0M
LTC3521
IN
FB1
V
OUT3
SW3
FB3
1.2V
SHDN1
SHDN2
SHDN3
PWM
221k
ON
600mA
OFF
100k
100k
PGOOD1
PGOOD2
PGOOD3
PWM
BURST
PGND1 GND PGND2
2.4
3.4
4.4
5.4
3521 TA01a
V
(V)
3521 TA01b
IN
3521f
ꢀ