LT3508
Dual Monolithic 1.4A
Step-Down Switching
Regulator
FEATURES DESCRIPTION
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Wide Input Voltage Range: 3.7V to 36V
The LT 3508 is a dual current mode PWM step-down
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Two 1.4A Output Switching Regulators with Internal
DC/DC converter with internal power switches capable of
Power Switches
generating two 1.4A outputs. The wide input voltage range
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Adjustable 250kHz to 2.5MHz Switching Frequency
of 3.7V to 36V makes the LT3508 suitable for regulating
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Synchronizable over the Full Frequency Range
power from a wide variety of sources, including automo-
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Anti-Phase Switching Reduces Ripple
tive batteries, 24V industrial supplies and unregulated wall
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Uses Small Inductors and Ceramic Capacitors
adapters. Both converters are synchronized to a single os-
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Accurate Programmable Undervoltage Lockout
cillator programmable up to 2.5MHz and run with opposite
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Independent Tracking, Soft-Start and Power Good
phases, reducing input ripple current. Its high operating
Circuits Ease Supply Sequencing
frequency allows the use of small, low cost inductors and
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Output Adjustable Down to 800mV
ceramic capacitors, resulting in low, predictable output
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Small 4mm 4mm 24-Pin QFN or 16-Pin Thermally
ripple. Each regulator has independent tracking and soft-
Enhanced TSSOP Surface Mount Packages
start circuits and generates a power good signal when its
output is in regulation, easing power supply sequencing
and interfacing with microcontrollers and DSPs.
APPLICATIONS
Cycle-by-cycle current limit, frequency foldback and ther-
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Automotive
mal shutdown provide protection against shorted outputs,
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DSP Power Supplies
and soft-start eliminates input current surge during start-
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Wall Transformer Regulation
up. The low current (<2A) shutdown mode enables easy
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DSL and Cable Modems
power management in battery-powered systems.
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PCI Express
L, LT, LTC, LTM, Linear Technology and the Linear logo are registered trademarks and
No R is a trademark of Linear Technology Corporation. All other trademarks are the
SENSE
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
Ef ciency
4.7F
V V
IN1 IN2 SHDN
95
OUT2
V = 12V
IN
BOOST1
BOOST2 5V
V = 5V
1.4A OUT2
90
0.22F 0.22F
6.8H
OUT1 10H
3.3V SW1
SW2
V = 3.3V
OUT1
1.4A
85
LT3508
35.7k 56.2k
80
FB1 FB2
V V
C1 C2
75
11.5k 51k
TRACK/SS1 PG1 43k 10.7k 10F
TRACK/SS2 PG2
70
100k
22F 150pF GND RT/SYNC
65
100pF
1nF 52.3k
0 0.5 1 1.5
LOAD CURRENT (A)
POWER
f = 700kHz
SW
3508 TA01a GOOD 3508 TA01b
3508fd
1
EFFICIENCY (%)LT3508
ABSOLUTE MAXIMUM RATINGS (Notes 1, 7)
V Pin Voltage ............................................(0.3V), 40V Storage Temperature Range
IN
BOOST Pin Voltage ...................................................60V QFN .................................................... 65C to 150C
BOOST Above SW Voltage ........................................30V TSSOP ............................................... 65C to 150C
SHDN, PG Voltage .....................................................40V Lead Temperature (Soldering, 10 sec)
TRACK/SS, FB, RT/SYNC, V Voltage ..........................6V TSSOP .............................................................. 300C
C
Operating Junction Temperature Range (Note 2)
LT3508E ............................................. 40C to 125C
LT3508I .............................................. 40C to 125C
LT3508H ............................................ 40C to 150C
PIN CONFIGURATION
TOP VIEW
TOP VIEW
TRACK/SS1 1 16 FB1
24 23 22 21 20 19
BOOST1 2 15 V
C1
FB1 1 18 FB2
SW1 3 14 PG1
TRACK/SS1 2 17 TRACK/SS2
V 4 13 RT/SYNC
IN1
17 GND 3 16 GND
25
GND
GND
V 5 12 SHDN
IN2 GND 4 15 GND
SW2 6 11 PG2 GND
GND 5 14
BOOST2 7 10 V GND 6 13 GND
C2
TRACK/SS2 8 9 FB2
7 8 9 10 11 12
FE PACKAGE
16-LEAD PLASTIC TSSOP
= 40C/W, = 10C/W
JA JC
UF PACKAGE
EXPOSED PAD (PIN 17) IS GND AND MUST BE SOLDERED TO PCB 24-LEAD (4mm 4mm) PLASTIC QFN
= 40C/W, = 10C/W
JA JC
EXPOSED PAD (PIN 25) IS GND AND MUST BE SOLDERED TO PCB
ORDER INFORMATION
LEAD FREE FINISH TAPE AND REEL PART MARKING* PACKAGE DESCRIPTION TEMPERATURE RANGE
LT3508EFE#PBF LT3508EFE#TRPBF 3508FE 16-Lead Plastic TSSOP 40C to 125C
LT3508IFE#PBF LT3508IFE#TRPBF 3508FE 16-Lead Plastic TSSOP 40C to 125C
LT3508HFE#PBF LT3508HFE#TRPBF 3508HFE 16-Lead Plastic TSSOP 40C to 150C
LT3508EUF#PBF LT3508EUF#TRPBF 3508 24-Lead (4mm 4mm) Plastic QFN 40C to 125C
LT3508IUF#PBF LT3508IUF#TRPBF 3508 24-Lead (4mm 4mm) Plastic QFN 40C to 125C
LT3508HUF#PBF LT3508HUF#TRPBF 3508H 40C to 150C
24-Lead (4mm 4mm) Plastic QFN
Consult LTC Marketing for parts speci ed with wider operating temperature ranges.*Temperature grades are identi ed by a label on the shipping container.
Consult LTC Marketing for information on non-standard lead based nish parts.
For more information on lead free part marking, go to: