LT3694/LT3694-1
36V, 2.6A Monolithic Buck
Regulator With Dual LDO
FEATURES
DESCRIPTION
The LT®3694/LT3694-1 are monolithic, current mode
DC/DC converters with dual, low dropout regulator con-
trollers. The switching converter is a step-down converter
capableofgeneratingupto2.6Aatitsoutput. Eachregula-
tor has independent track/soft-start circuits simplifying
power supply sequencing and interfacing with micro-
controllers and DSPs.
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Wide Input Range: 4V to 36V
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Overvoltage Shutdown Protects Circuit Through
70V Transients
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2.6A Output Switching Regulator with Internal
Power Switch
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Dual, Low Dropout, Linear Regulator Controllers
with Programmable Current Limit
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Tracking/Soft-Start Inputs and Power Good Output
The switching frequency is set with a single resistor with a
range of 250kHz to 2.5MHz. The high switching frequency
permits the use of small inductors and ceramic capacitors
leadingtoverysmalltripleoutputsolutions. Theconstant-
switching frequency, combined with low impedance ce-
ramic capacitors, results in low, predictable output ripple.
Protectioncircuitrysensesthecurrentinthepowerswitch
and external Schottky catch diode to protect the LT3694
against short-circuit conditions. Frequency foldback and
thermal shutdown provide additional protection.
Simplify Soft-Start and Supply Sequencing
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Uses Small Inductors and Ceramic Capacitors
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V
= 0.75V (Buck and LDOs)
OUT(MIN)
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Adjustable 250kHz to 2.5MHz Switching Frequency
Accurate Enable Threshold Allows User
Programmable Undervoltage Lockout
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Options for Clock Synchronization (LT3694) or Clock
Output to Enable Synchronization to Other Switching
Regulators (LT3694-1)
Thermally Enhanced 28-Lead 4mm × 5mm QFN and
20-Lead TSSOP Packages
With its wide input voltage range of 4V to 36V, the LT3694
regulatesabroadarrayofpowersourcesfrom4-cellbatteries
and5Vlogicrailstounregulatedwalltransformers,leadacid
batteriesanddistributedpowersupplies.TheLT3694canbe
synchronized to an external clock with the SYNC pin while
the LT3694-1 offers a CLKOUT pin allowing other DC/DC
converters to synchronize to the LT3694-1 clock.
APPLICATIONS
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Automotive
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Industrial
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DSL and Cable Modems
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Distributed Power Regulation
L, LT, LTC, LTM, Linear Technology, the Linear logo and Burst Mode are registered trademarks
of Linear Technology Corporation. All other trademarks are the property of their respective owners.
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Wall Transformer Regulation
TYPICAL APPLICATION
V
Efficiency at VOUT = 3.3V
IN
4.5V TO 36V
4.7μF
V
EN/UVLO
BIAS BST
IN
100
0.22μF
B340A
f
= 800kHz
SW
4.7μH
OUT1
3.3V
1.7A
TRK/SS1
TRK/SS2
TRK/SS3
SW
V
V
= 4.5V
= 12V
IN
90
80
70
60
50
1nF
34k
10k
IN
DA
FB1
0.1Ω
47μF
V
= 36V
LT3694
IN
330pF
OUT1
LIM2
DRV2
41.2k
V
C1
OUT2
2.5V
450mA
OUT1
LIM3
DRV3
0.1Ω
24.9k
10.7k
OUT3
1.8V
450mA
2.2μF
FB2
SYNC
15.4k
2.2μF
FB3
PGOOD
RT
0
1
2
3
51.1k
11k
I
(A)
OUT
GND
36941 TA01b
f
= 800kHz
SW
36941 TA01a
36941fa
1