FEATURES
n
n
n
n
n
n
n
n
LT3570
1.5A Buck Converter,
1.5A Boost Converter and
LDO Controller
DESCRIPTION
The LT
®
3570 is a buck and boost converter with internal
power switches and LDO controller. Each converter is
designed with a 1.5A current limit and an input range
from 2.5V to 36V, making the LT3570 ideal for a wide
variety of applications. Switching frequencies up to 2MHz
are programmed with an external timing resistor and the
oscillator can be synchronized to an external clock up to
2.75MHz.
The LT3570 features a programmable soft-start function
that limits the feedback voltage during start-up helping
prevent overshoot and limiting inrush current. The LDO
controller is capable of delivering up to 10mA of base
current to an external NPN transistor.
L,
LT, LTC and LTM are registered trademarks of Linear Technology Corporation.
All other trademarks are the property of their respective owners.
2.5V to 36V Input Voltage Range
Programmable Switching Frequency
from 500kHz to 2MHz
Synchronizable Up to 2.75MHz
V
OUT(MIN)
: 0.8V
Independent Soft-Start for Each Converter
Separate V
IN
Supplies for Each Converter
Duty Cycle Range: 0% to 90% at 1MHz
Available in 24-Lead (4mm
×
4mm) QFN and
20-Lead TSSOP Packages
APPLICATIONS
n
n
n
n
n
Cable and Satellite Set-Top Boxes
Automotive Systems
Telecom Systems
“Dying Gasp” Systems
TFT LCD Displays
TYPICAL APPLICATION
V
IN
5V
10μF
SHDN1
SHDN2
SHDN3
D1
6.8μH
SW1
143k
10μF
10.0k
22k
NPN_DRV
1nF
10nF
FB3
GND
22.1k
R
T
SYNC
15.8k
3570 TA01a
V
IN1
V
IN2
V
IN3
BIAS
SHDN1
SHDN2
SHDN3
BOOST
100nF
SW2
D2
FB2
SS2
V
C2
22k
1nF
D3
V
OUT2
3.3V
1A
32.4k
EFFICIENCY (%)
90
85
80
75
Q1
V
OUT3
2.5V
100mA
2.2μF
10.2k
70
0
0.2
f
SW
= 1.2MHz
VIN = 5V
V
OUT1
= 12V
V
OUT2
= 3.3V
V
OUT3
= 2.5V
I
OUT1
= 275mA
I
OUT3
= 100mA
100
95
Efficiency
3.3μH
V
OUT1
12V
275mA
22μF
10nF
10.2k
FB1
SS1
V
C1
LT3570
0.4
0.6
I
OUT2
(A)
0.8
1.0
3570 TA01b
3570fa
1
LINER [ LINEAR TECHNOLOGY ]
