FEATURES
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LT3694/LT3694-1
36V, 2.6A Monolithic Buck
Regulator With Dual LDO
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
capable of generating up to 2.6A at its output. Each regu-
lator has independent track/soft-start circuits simplifying
power supply sequencing and interfacing with micro-
controllers and DSPs.
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
leading to very small triple output solutions. The constant-
switching frequency, combined with low impedance ce-
ramic capacitors, results in low, predictable output ripple.
Protection circuitry senses the current in the power switch
and external Schottky catch diode to protect the LT3694
against short-circuit conditions. Frequency foldback and
thermal shutdown provide additional protection.
With its wide input voltage range of 4V to 36V, the LT3694
regulates a broad array of power sources from 4-cell batteries
and 5V logic rails to unregulated wall transformers, lead acid
batteries and distributed power supplies. The LT3694 can be
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.
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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Wide Input Range: 4V to 36V
Overvoltage Shutdown Protects Circuit Through
70V Transients
2.6A Output Switching Regulator with Internal
Power Switch
Dual, Low Dropout, Linear Regulator Controllers
with Programmable Current Limit
Tracking/Soft-Start Inputs and Power Good Output
Simplify Soft-Start and Supply Sequencing
Uses Small Inductors and Ceramic Capacitors
V
OUT(MIN)
= 0.75V (Buck and LDOs)
Adjustable 250kHz to 2.5MHz Switching Frequency
Accurate Enable Threshold Allows User
Programmable Undervoltage Lockout
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
APPLICATIONS
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Automotive
Industrial
DSL and Cable Modems
Distributed Power Regulation
Wall Transformer Regulation
TYPICAL APPLICATION
V
IN
4.5V TO 36V
Efficiency at V
OUT
= 3.3V
4.7µF
EN/UVLO
TRK/SS1
TRK/SS2
TRK/SS3
LIM2
DRV2
24.9k
FB2
SYNC
10.7k
51.1k
PGOOD
RT
f
SW
= 800kHz
GND
FB3
11k
36941 TA01a
V
IN
BIAS
BST
SW
DA
FB1
V
C1
LIM3
0.22µF
B340A
4.7µH
34k
100
1nF
0.1
OUT1
3.3V
1.7A
47µF
EFFICIENCY (%)
f
SW
= 800kHz
V
IN
= 4.5V
V
IN
= 12V
V
IN
= 36V
90
OUT1
OUT2
2.5V
450mA
LT3694
41.2k
330pF
10k
OUT1
80
70
2.2µF
DRV3
0.1
15.4k
2.2µF
OUT3
1.8V
450mA
60
50
0
1
I
OUT
(A)
2
3
36941 TA01b
36941fb
1
LINER [ LINEAR TECHNOLOGY ]
