LT3508
Dual Monolithic 1.4A
Step-Down Switching
Regulator
FEATURES
DESCRIPTION
The LT®3508 is a dual current mode PWM step-down
DC/DC converter with internal power switches capable of
generatingtwo1.4Aoutputs. Thewideinputvoltagerange
of 3.7V to 36V makes the LT3508 suitable for regulating
power from a wide variety of sources, including automo-
tivebatteries,24Vindustrialsuppliesandunregulatedwall
adapters. Bothconvertersaresynchronizedtoasingleos-
cillatorprogrammableupto2.5MHzandrunwithopposite
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.
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Wide Input Voltage Range: 3.7V to 36V
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Two 1.4A Output Switching Regulators with Internal
Power Switches
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Adjustable 250kHz to 2.5MHz Switching Frequency
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Synchronizable over the Full Frequency Range
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Anti-Phase Switching Reduces Ripple
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Uses Small Inductors and Ceramic Capacitors
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Accurate Programmable Undervoltage Lockout
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Independent Tracking, Soft-Start and Power Good
Circuits Ease Supply Sequencing
Output Adjustable Down to 800mV
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Small 4mm × 4mm 24-Pin QFN or 16-Pin Thermally
Enhanced TSSOP Surface Mount Packages
APPLICATIONS
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Automotive
Cycle-by-cycle current limit, frequency foldback and ther-
malshutdownprovideprotectionagainstshortedoutputs,
and soft-start eliminates input current surge during start-
up. The low current (<2μA) shutdown mode enables easy
power management in battery-powered systems.
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DSP Power Supplies
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Wall Transformer Regulation
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DSL and Cable Modems
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PCI Express
, LT, LTC and LTM are registered trademarks of Linear Technology Corporation.
All other trademarks are the property of their respective owners.
TYPICAL APPLICATION
3.3V and 5V Dual Output Step-Down Converter with Output Sequencing
V
IN
ON OFF
5.6V TO 36V
Efficiency
4.7ꢀF
V
SHDN
IN
95
90
85
80
75
70
65
OUT2
5V
V
= 12V
IN
BOOST1
BOOST2
1.4A
V
V
= 5V
OUT2
OUT1
0.22ꢀF
0.22ꢀF
6.8ꢀH
10ꢀH
OUT1
3.3V
1.4A
SW1
SW2
= 3.3V
LT3508
35.7k
56.2k
FB1
FB2
V
V
C2
C1
11.5k
22ꢀF
51k
TRACK/SS1
TRACK/SS2
PG1
PG2
43k
10ꢀF
10.7k
GND R /SYNC
100k
150pF
1nF
T
100pF
52.3k
= 700kHz
0
0.5
1
1.5
LOAD CURRENT (A)
POWER
GOOD
f
SW
3508 TA01a
3508 TA01b
3508fb
1