Document
LTC3520
Synchronous 1A Buck-Boost and 600mA
Buck Converters
FEATURES
n Dual High Efficiency DC/DC Converters: Buck-Boost (VOUT: 2.2V to 5.25V, IOUT = 1A at VOUT = 3.3V, VIN ≥ 3V) Buck (VOUT: 0.8V to VIN, IOUT = 600mA)
n 2.2V to 5.5V Input Voltage Range n Pin-Selectable Burst Mode® Operation n Uncommitted Gain Block for LDO Controller, Battery
Good Indication or Sequencing n Programmable 100kHz to 2MHz Switching Frequency n 55μA Total Quiescent Current for Both Converters in
Burst Mode Operation n Thermal and Overcurrent Protection n <1μA Quiescent Current in Shutdown n 24-Lead 4mm × 4mm QFN Package
APPLICATIONS
n Portable Media Players n Digital Cameras n Handheld PCs, PDAs n GPS Receivers
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, 6166527, 6304066, 6404251, 6580258.
DESCRIPTION
The LTC®3520 combines 1A buck-boost and 600mA synchronous buck DC/DC converters in a tiny 4mm × 4mm package. A programmable switching frequency allows the efficiency to be optimized while minimizing the solution footprint. Both converters feature soft-start and current limit protection. The uncommitted gain block can be configured as an LDO or utilized as a battery-good comparator.
The buck converter is current mode controlled with internal synchronous rectification to improve efficiency. Pin-selectable Burst Mode operation can be enabled to improve light load efficiency, or the buck converter can be operated in low noise PWM mode for sensitive applications.
The buck-boost converter provides continuous conduction operation to maximize efficiency and minimize noise. At light loads, use of Burst Mode operation will improve efficiency.
The LTC3520 provides a <1μA shutdown mode and overtemperature shutdown on both converters. The LTC3520 is available in a low profile (0.75mm) 24-lead 4mm × 4mm QFN package.
TYPICAL APPLICATION
3.3V at 500mA, 1.8V at 600mA and 1.5V at 200mA Converter
VIN 2.2V TO
5.5V
VOUT2 1.8V
600mA
10μF
22μF 255k 200k
BURST
4.7μH 27pF
0.01μF 54.9k
PWM
PVIN1 PVIN2 PVIN3 SVIN SW1A SW1B
SW2
VOUT1
VC1 FB2
SS2
FB1
LTC3520
SS1
RT
PWM1 PWM2
AOUT
4.7μH 470pF
15k 0.01μF VOUT2
SD3
OFF ON
SD2
SD1
AIN
PGND1 SGND PGND2
56pF 1M
10k 309k
33pF 100k
110k
47μF
VOUT1 3.3V 500mA 1A FOR VIN ≥ 3V
VOUT 1.5V 200mA
4.7μF
3520 TA01
EFFICIENCY (%)
Efficiency vs VIN
100
BUCK-BOOST
95
IOUT = 150mA
BUCK
90
IOUT = 250mA
85
80
75
70 2.2 2.7 3.2 3.7 4.2 4.7 5.2
VIN (V)
3520 TA01b
3520fa
1
LTC3520
ABSOLUTE MAXIMUM RATINGS
(Note 1)
PVIN1, PVIN2, PVIN3, SVIN Voltage................ –0.3V to 6V SW1A, SW1B, SW2 Voltage
DC............................................................ –0.3V to 6V Pulsed <100ns ............................................ –1V to 7V Voltage, All Other Pins ................................. –0.3V to 6V Operating Junction Temperature Range (.