LTC3521 Datasheet, PDF (1/20 Pages) Linear Technology – Wide VIN, 1A Buck-Boost DC/DC and Dual 600mA Buck DC/DC Converters

LTC3521
Wide V_IN, 1A Buck-Boost
DC/DC and Dual 600mA
Buck DC/DC Converters
Features
n _{Three High Efficiency DC/DC Converters:}
Buck-Boost (V_OUT: 1.8V to 5.25V, I_OUT: 1A)
Dual Buck (V_OUT: 0.6V to V_IN, I_OUT: 600mA)
n _{1.8V to 5.5V Input Voltage Range}
n _{Pin-Selectable Burst Mode}^® _Operation
n _{30µA Total Quiescent Current in Burst Mode}
Operation
n _{Independent Power Good Indicator Outputs}
n _{Integrated Soft-Start}
n _{Thermal and Overcurrent Protection}
n _{<2µA Current in Shutdown}
n _{Small 4mm × 4mm QFN and Thermally Enhanced}
TSSOP Packages
Applications
n _{Bar Code Readers}
n _{Medical Instruments}
n _{Handy Terminals}
n _{PDAs, Handheld PCs}
n _{GPS Receivers}
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.
Description
The LTC^®3521 combines a 1A buck-boost DC/DC converter
and dual 600mA synchronous buck DC/DC converters. The
1.1MHz switching frequency minimizes the solution foot-
print while maintaining high efficiency. All three converters
feature soft-start and internal compensation to minimize
the solution footprint and simplify the design process.
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.
The buck-boost converter features continuous conduction
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.
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.
Typical Application
V_IN
2.4V TO 4.2V
+
Li-Ion
V_OUT1
3.3V
800mA
(1A, V_IN > 3.0V)
22µF
4.7µF
4.7µH
1.0M
221k ON
OFF
PWM
BURST
PV_IN1 PV_IN2
4.7µH
SW1A
SW2
SW1B
FB2
V_OUT1
LTC3521
FB1
SHDN1
SW3
SHDN2
FB3
SHDN3 PGOOD1
PWM
PGOOD2
PGOOD3
PGND1 GND PGND2
4.7µH
3521 TA01a
137k
68.1k
100k
100k
V_OUT2
1.8V
10µF ^600mA
V_OUT3
1.2V
10µF ^600mA
100
98
96
94
92
90
88
86
84
82
80
78
76
74
72
70
2.4
Efficiency vs V_IN
V_OUT1 = 3.3V
I_OUT = 500mA
V_OUT2 = 1.8V
I_OUT = 200mA
V_OUT3 = 1.2V
I_OUT = 200mA
3.4
4.4
V_IN (V)
5.4
3521 TA01b
3521f