LTC3520
Synchronous 1A
Buck-Boost and 600mA
Buck Converters
FEATURES
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.
■
Dual High Efficiency DC/DC Converters:
Buck-Boost (V : 2.2V to 5.25V, I
= 1A at
OUT
IN
OUT
V
= 3.3V, V ≥ 3V)
OUT
Buck (V : 0.8V to V , I
= 600mA)
OUT
IN OUT
■
■
■
2.2V to 5.5V Input Voltage Range
Pin-Selectable Burst Mode® Operation
Uncommitted Gain Block for LDO Controller,
Battery Good Indication or Sequencing
Programmable 100kHz to 2MHz Switching Frequency
55µA Total Quiescent Current for Both Converters in
Burst Mode Operation
■
■
Thebuckconverteriscurrentmodecontrolledwithinternal
synchronousrectificationtoimproveefficiency.Pin-select-
ableBurstModeoperationcanbeenabledtoimprovelight
load efficiency, or the buck converter can be operated in
low noise PWM mode for sensitive applications.
■
■
■
Thermal and Overcurrent Protection
<1µA Quiescent Current in Shutdown
24-Lead 4mm × 4mm QFN Package
The buck-boost converter provides continuous conduc-
tion operation to maximize efficiency and minimize noise.
At light loads, use of Burst Mode operation will improve
efficiency.
APPLICATIONS
■
Portable Media Players
■
Digital Cameras
The LTC3520 provides a <1µA shutdown mode and over-
temperature shutdown on both converters. The LTC3520
is available in a low profile (0.75mm) 24-lead 4mm ×
4mm QFN package.
■
Handheld PCs, PDAs
GPS Receivers
■
, 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 5481178, 6166527, 6304066, 6404251, 6580258.
TYPICAL APPLICATION
3.3V at 500mA, 1.8V at 600mA and 1.5V at 200mA Converter
Efficiency vs V
IN
V
IN
100
95
90
85
80
75
70
4.7µH
2.2V TO
5.5V
22µF
PV
IN1
PV
IN2
PV
IN3
SV SW1A
IN
BUCK-BOOST
I = 150mA
OUT
V
3.3V
4.7µH
OUT1
SW1B
V
OUT2
1.8V
600mA
SW2
V
OUT1
470pF
500mA
1A FOR
255k
27pF
56pF
10k
BUCK
OUT
10µF
47µF
V
C1
V
IN
≥ 3V
1M
I
= 250mA
FB2
SS2
15k
0.01µF
200k
FB1
SS1
0.01µF
309k
LTC3520
54.9k
R
T
V
OUT2
PWM1
PWM2
SD3
A
OUT
V
BURST
PWM
OUT
1.5V
200mA
33pF
100k
110k
SD2
OFF ON
4.7µF
SD1
A
IN
2.7
3.2
4.2
(V)
4.7
5.2
2.2
3.7
PGND1 SGND PGND2
V
IN
3520 TA01
3520f
1