FEATURES
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LT3507
Triple Monolithic Step-Down
Regulator with LDO
DESCRIPTION
The LT
®
3507 is a triple, current mode, DC/DC converter
with internal power switches and a low dropout regulator.
The switching converters are step-down converters capable
of generating one 2.4A output and two 1.5A outputs. All
three converters are synchronized to a single oscillator.
The 2.4A output runs with opposite phase to the other two
converters, reducing input ripple current. Each regulator
has independent shutdown and soft-start circuits, and
generates a power good signal when its output is in regu-
lation, easing power supply sequencing and interfacing
with microcontrollers and DSPs.
The switching frequency is set with a single resistor yielding
a range of 250kHz to 2.5MHz. The high switching frequency
allows the use of small inductors and capacitors resulting
in a very small triple output supply. The constant switching
frequency, combined with low impedance ceramic capaci-
tors, results in low, predictable output ripple. With its wide
input voltage range of 4V to 36V, the LT3507 regulates a
broad array of power sources including 5V logic rails,
unregulated wall transformers, lead acid batteries and
distributed power supplies.
Wide Input Range: 4V to 36V
One 2.4A and Two 1.5A Output Switching
Regulators with Internal Power Switches
Low Dropout Linear Regulator with External
Transistor
Antiphase Switching Reduces Ripple
Independent Run, Tracking/Soft-Start, and Power
Good Indicators Ease Supply Sequencing
Uses Small Inductors and Ceramic Capacitors
Adjustable, 250kHz to 2.5MHz Switching Frequency,
Synchronizable Over the Full Range
User Programmable Overvoltage and Undervoltage
Lockouts
Thermally Enhanced, 38-Lead 5mm
×
7mm QFN
Package
DSL and Cable Modems
Distributed Power Regulation
DSP Power
Automotive
APPLICATIONS
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L,
LT, LTC, LTM, Linear Technology and the Linear logo are registered trademarks of Linear
Technology Corporation. All other trademarks are the property of their respective owners.
TYPICAL APPLICATION
5V, 3.3V, 2.5V and 1.8V Step-Down Regulator
V
IN
6V TO 36V
22μF
V
IN1
BOOST1
V
OUT1
1.8V
2.4A
4.7μH
0.22μF
SW1
18.7k
100μF
15k
18.7k
680pF
V
C1
0.22μF BOOST3
SW3
53.6k
22μF
10.2k
24.3k
680pF
V
C3
R
T
/SYNC
DRIVE
24.3k
FB4
GND
11.5k
2.2μF
107k
V
OUT4
2.5V
0.2A
FB3
BIAS
LT3507
FB2
1000pF
V
C2
11.5k
16.2k
35.7k
10μH
FB1
SW2
V
OUT2
3.3V
1.3A
22μF
0.22μF
V
IN2
V
IN3
BOOST2
Start-Up Waveforms—Coincident Tracking
V
OUT3
V
OUT2
V
OUT4
V
OUT1
1V/DIV
V
OUT2
V
OUT3
5V
1.5A
15μH
1ms/DIV
3507 TA01b
f
SW
= 450kHz
3507 TA01a
3507fa
1
LINEAR_DIMENSIONS [ LINEAR DIMENSIONS SEMICONDUCTOR ]
