Triple Monolithic Step-Down
Regulator with LDO
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
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
n Thermally Enhanced, 38-Lead 5mm × 7mm QFN
n DSL and Cable Modems
n Distributed Power Regulation
n DSP Power
L, LT, LTC and LTM are registered trademarks of Linear Technology Corporation.
All other trademarks are the property of their respective owners.
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.
6V TO 36V
5V, 3.3V, 2.5V and 1.8V Step-Down Regulator
VIN1 VIN2 VIN3
fSW = 450kHz
Start-Up Waveforms—Coincident Tracking