LT3507_15 Datasheet, PDF (1/28 Pages) Linear Technology – Triple Monolithic Step-Down Regulator with LDO

LT3507
Triple Monolithic Step-Down
Regulator with LDO
FEATURES
n _{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
APPLICATIONS
n _{DSL and Cable Modems}
n _{Distributed Power Regulation}
n _{DSP Power}
n _Automotive
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.
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.
TYPICAL APPLICATION
V_IN
6V TO 36V
V_OUT1
1.8V
2.4A
V_OUT3
5V
1.5A
5V, 3.3V, 2.5V and 1.8V Step-Down Regulator
22μF
4.7μH
V_IN1 V_IN2 V_IN3
BOOST1
BOOST2
0.22μF
SW1
0.22μF
18.7k
100μF
15k
18.7k
V_OUT2
15μH
FB1
680pF
V_C1
LT3507
0.22μF ^BOOST3
SW3
53.6k
10μH
SW2
FB2
1000pF
16.2k
V_C2
35.7k
11.5k
22μF
10.2k
FB3
680pF
24.3k
V_C3
R_T/SYNC
107k
GND
BIAS
DRIVE
FB4
24.3k
11.5k
f_SW = 450kHz
V_OUT2
3.3V
1.3A
22μF
2.2μF
V_OUT4
2.5V
0.2A
3507 TA01a
Start-Up Waveforms—Coincident Tracking
1V/DIV
V_OUT3
V_OUT2
V_OUT4
V_OUT1
1ms/DIV
3507 TA01b
3507fa
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