FEATURES
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LT3508
Dual Monolithic 1.4A
Step-Down Switching
Regulator
DESCRIPTION
The LT
®
3508 is a dual current mode PWM step-down
DC/DC converter with internal power switches capable of
generating two 1.4A outputs. The wide input voltage range
of 3.7V to 36V makes the LT3508 suitable for regulating
power from a wide variety of sources, including automo-
tive batteries, 24V industrial supplies and unregulated wall
adapters. Both converters are synchronized to a single os-
cillator programmable up to 2.5MHz and run with opposite
phases, reducing input ripple current. Its high operating
frequency allows the use of small, low cost inductors and
ceramic capacitors, resulting in low, predictable output
ripple. Each regulator has independent tracking 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.
Cycle-by-cycle current limit, frequency foldback and ther-
mal shutdown provide protection against shorted outputs,
and soft-start eliminates input current surge during start-
up. The low current (<2μA) shutdown mode enables easy
power management in battery-powered systems.
, LT, LTC and LTM are registered trademarks of Linear Technology Corporation.
All other trademarks are the property of their respective owners.
Wide Input Voltage Range: 3.7V to 36V
Two 1.4A Output Switching Regulators with Internal
Power Switches
Adjustable 250kHz to 2.5MHz Switching Frequency
Synchronizable over the Full Frequency Range
Anti-Phase Switching Reduces Ripple
Uses Small Inductors and Ceramic Capacitors
Accurate Programmable Undervoltage Lockout
Independent Tracking, Soft-Start and Power Good
Circuits Ease Supply Sequencing
Output Adjustable Down to 800mV
Small 4mm
×
4mm 24-Pin QFN or 16-Pin Thermally
Enhanced TSSOP Surface Mount Packages
APPLICATIONS
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Automotive
DSP Power Supplies
Wall Transformer Regulation
DSL and Cable Modems
PCI Express
TYPICAL APPLICATION
3.3V and 5V Dual Output Step-Down Converter with Output Sequencing
V
IN
5.6V TO 36V
4.7μF
V
IN
BOOST1
OUT1
3.3V
1.4A
6.8μH
0.22μF
SW1
LT3508
35.7k
FB1
V
C1
11.5k
51k
TRACK/SS1
TRACK/SS2
GND
FB2
V
C2
PG1
PG2
43k
10.7k
100k
100pF
POWER
GOOD
10μF
56.2k
SW2
EFFICIENCY (%)
85
80
75
70
65
SHDN
BOOST2
0.22μF
10μH
OUT2
5V
1.4A
95
90
V
IN
= 12V
V
OUT2
= 5V
V
OUT1
= 3.3V
ON OFF
Efficiency
22μF
150pF
1nF
R
T
/SYNC
52.3k
0
0.5
1
LOAD CURRENT (A)
1.5
3508 TA01b
f
SW
= 700kHz
3508 TA01a
3508fb
1
LINER [ LINEAR TECHNOLOGY ]
