LTC3522_15 Datasheet, PDF (1/20 Pages) Linear Technology – Synchronous 400mA Buck-Boost and 200mA Buck Converters

LTC3522
Synchronous 400mA
Buck-Boost and 200mA
Buck Converters
FEATURES
■ _{Dual High Efficiency DC/DC Converters:}
Buck-Boost (V_OUT: 2.2V to 5.25V, I_OUT: 400mA
for V_IN > 3V, V_OUT = 3.3V)
Buck (V_OUT: 0.6V to V_IN, I_OUT: 200mA)
■ _{2.4V to 5.5V Input Voltage Range}
■ _{Pin Selectable Burst Mode}^® _Operation
■ _{25μA Total Quiescent Current for Both Converters in}
Burst Mode Operation
■ _{Independent Power Good Indicator Outputs}
■ _{Integrated Soft-Start}
■ _{Thermal and Overcurrent Protection}
■ _{<1μA Quiescent Current in Shutdown}
■ _{Small 0.75mm × 3mm × 3mm QFN Package}
APPLICATIONS
■ _{Flash-Based MP3 Players}
■ _{Medical Instruments}
■ _{Digital Cameras}
■ _{PDAs, Handheld PCs}
■ _{Personal Navigation Devices}
, LT, LTC, LTM 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 6404251 and 6166527.
DESCRIPTION
The LTC^®3522 combines a 400mA buck-boost DC/DC con-
verter with a 200mA synchronous buck DC/DC converter in
a tiny 3mm × 3mm package. The 1MHz switching frequency
minimizes the solution footprint while maintaining high
efficiency. Both converters feature internal soft-start and
compensation, simplifying the design process.
The buck converter is current mode controlled and utilizes
an internal synchronous rectifier for high efficiency. The
buck converter supports 100% duty cycle operation to
extend battery life. If the PWM pin is held low, the buck
converter automatically transitions from Burst Mode opera-
tion to PWM mode. With the PWM pin held high, the buck
converter remains in low noise, 1MHz PWM mode.
The buck-boost converter provides continuous conduc-
tion operation to maximize efficiency and minimize noise.
At light loads, the buck-boost converter can be placed in
Burst Mode operation to improve efficiency and reduce
no-load standby current.
The LTC3522 provides a 1μA shutdown mode, overtem-
perature shutdown and current limit protection on both
converters. The LTC3522 is available in a 16-pin low profile
3mm × 3mm QFN package.
TYPICAL APPLICATION
V_IN
2.4V TO 4.2V ₊
Li-Ion
V_OUT2
1.8V
200mA
6.8μF
4.7μF
137k
L1
8.2μH
12pF
68.1k
ON
OFF
PWM
BURST
L1: COILCRAFT MSS6132-8.2μH
L2: COILCRAFT MSS6132-4.7μH
PV_IN1 PV_IN2
SW2
SW1A
L2
4.7μH
SW1B
LTC3522
FB2
V_OUT1
SHDN2
1M
SHDN1
FB1
PGOOD2
432k
PWM
PGOOD1
PGND1 GND PGND2
3522 TA01a
V_OUT1
3.3V
300mA
4.7μF
(400mA
V_IN > 3V)
100
98
96
94
92
90
88
86
84
82
80
78
76
74
72
70
2.4
Efficiency vs V_IN
BUCK-BOOST
I_OUT = 100mA
V_OUT = 3.3V
BUCK
I_OUT = 100mA
V_OUT = 1.8V
3.4
4.4
V_IN (V)
5.4
3522 TA01b
3522fa
1