Features
Wide Input Range: 4V to 36V
n One 2.4A and Two 1.5A Output Switching
Regulators with Internal Power Switches
n Low Dropout Linear Regulator with External
Transistor
n Antiphase Switching Reduces Ripple
n Independent Run, Tracking/Soft-Start, and Power
Good Indicators Ease Supply Sequencing
n Uses Small Inductors and Ceramic Capacitors
n Adjustable, 250kHz to 2.5MHz Switching Frequency,
Synchronizable Over the Full Range
n User Programmable Overvoltage and Undervoltage
Lockouts
n Thermally Enhanced, 38-Lead 5mm × 7mm QFN
Package
n
Applications
DSL and Cable Modems
Distributed Power Regulation
n DSP Power
n Automotive
n
n
L, LT, LTC, LTM, Burst Mode, Linear Technology and the Linear logo are registered trademarks of
Linear Technology Corporation. All other trademarks are the property of their respective owners.
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 regulation, 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 capacitors, 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.
Typical Application
5V, 3.3V, 2.5V and 1.8V Step-Down Regulator
Start-Up Waveforms—Coincident Tracking
VIN
6V TO 36V
22µF
VIN1
VIN2
BOOST1
VOUT3
BOOST2
0.22µF
4.7µH
VOUT1
1.8V
2.4A
VIN3
SW1
0.22µF
18.7k
100µF
15k
18.7k
VOUT2
VOUT3
5V
1.5A
VC1
1000pF
VC2
53.6k
FB3
10.2k
24.3k
22µF
FB2
SW3
22µF
35.7k
LT3507
VOUT4
VOUT1
VOUT2
3.3V
1.3A
680pF
0.22µF BOOST3
15µH
10µH
SW2
FB1
VOUT2
1V/DIV
1ms/DIV
11.5k
3507 TA01b
BIAS
VC3
16.2k
DRIVE
680pF
107k
RT/SYNC
FB4
GND
24.3k
11.5k
2.2µF
VOUT4
2.5V
0.2A
fSW = 450kHz
3507 TA01a
For more information www.linear.com/LT3507
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