LT3694/LT3694-1
1
36941fb
TYPICAL APPLICATION
DESCRIPTION
36V, 2.6A Monolithic Buck
Regulator With Dual LDO
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.
FEATURES
APPLICATIONS
n
Wide Input Range: 4V to 36V
n
Overvoltage Shutdown Protects Circuit Through
70V Transients
n
2.6A Output Switching Regulator with Internal
Power Switch
n
Dual, Low Dropout, Linear Regulator Controllers
with Programmable Current Limit
n
Tracking/Soft-Start Inputs and Power Good Output
Simplify Soft-Start and Supply Sequencing
n
Uses Small Inductors and Ceramic Capacitors
n
V
OUT(MIN)
= 0.75V (Buck and LDOs)
n
Adjustable 250kHz to 2.5MHz Switching Frequency
n
Accurate Enable Threshold Allows User
Programmable Undervoltage Lockout
n
Options for Clock Synchronization (LT3694) or Clock
Output to Enable Synchronization to Other Switching
Regulators (LT3694-1)
n
Thermally Enhanced 28-Lead 4mm × 5mm QFN and
20-Lead TSSOP Packages
n
Automotive
n
Industrial
n
DSL and Cable Modems
n
Distributed Power Regulation
n
Wall Transformer Regulation
SW
FB3
PGOOD
RT
FB2
SYNC
V
IN
V
C1
BIAS
V
IN
4.5V TO 36V
f
SW
= 800kHz
GND
LT3694
36941 TA01a
TRK/SS1
TRK/SS2
TRK/SS3
LIM2
DRV2
DA
FB1
LIM3
DRV3
EN/UVLO BST
OUT1
3.3V
1.7A
OUT3
1.8V
450mA
OUT2
2.5V
450mA
47µF
34k
B340A
4.7µH
0.22µF
10k
OUT1
OUT1
41.2k
15.4k
24.9k
10.7k
51.1k
11k
2.2µF
4.7µF
2.2µF
1nF
0.1Ω
0.1Ω
330pF
Efficiency at V
OUT
= 3.3V
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.
90
80
70
60
50
100
I
OUT
(A)
EFFICIENCY (%)
0 1 2 3
36941 TA01b
V
IN
= 4.5V
V
IN
= 12V
V
IN
= 36V
f
SW
= 800kHz
