LT3694/LT3694-1
36V, 2.6A Monolithic Buck
Regulator With Dual LDO
DESCRIPTION
FEATURES
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
The LT®3694/LT3694-1 are monolithic, current mode
DC/DC converters with dual, low dropout regulator controllers. The switching converter is a step-down converter
capable of generating up to 2.6A at its output. Each regulator has independent track/soft-start circuits simplifying
power supply sequencing and interfacing with microcontrollers and DSPs.
n
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 constantswitching frequency, combined with low impedance ceramic 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.
APPLICATIONS
Automotive
Industrial
n DSL and Cable Modems
n Distributed Power Regulation
n Wall Transformer Regulation
n
n
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.
TYPICAL APPLICATION
Efficiency at VOUT = 3.3V
4.7µF
EN/UVLO
1nF
OUT1
0.1Ω
VIN BIAS
TRK/SS1
TRK/SS2
LT3694
DA
FB1
VC1
DRV2
OUT2
2.5V
450mA
LIM3
2.2µF
DRV3
24.9k
FB2
SYNC
10.7k
51.1k
fSW = 800kHz
100
4.7µH
B340A
41.2k
OUT1
3.3V
1.7A
47µF
10k
0.1Ω
FB3
GND
34k
330pF
15.4k
PGOOD
RT
0.22µF
SW
TRK/SS3
LIM2
BST
11k
OUT1
2.2µF
OUT3
1.8V
450mA
fSW = 800kHz
VIN = 4.5V
90
EFFICIENCY (%)
VIN
4.5V TO 36V
VIN = 12V
VIN = 36V
80
70
60
50
0
1
2
IOUT (A)
3
36941 TA01b
36941 TA01a
36941fb
1
