LT3740 Datasheet, PDF (1/20 Pages) Linear Technology – Wide Operating Range, Valley Mode, No RSENSE™ Synchronous Step-Down Controller

LT3740
FEATURES
Wide Operating Range,
Valley Mode, No R_SENSE™
Synchronous Step-Down Controller
DESCRIPTION
n _{Wide VIN Range: 2.2V to 22V}
n _{Internal Boost Provides 6V Gate Drive}
For V_IN Down to 2.2V
n _{No Sensing Resistor Required}
n _{Dual N-Channel MOSFET Synchronous Drive}
n _{Valley Current Mode Control}
n _{Optimized for High Step-Down Ratio}
n _{Power Good Output Voltage Monitor}
n _{0.8V Reference}
n _{Three Pin-Selected Current Limit Levels}
n _{Constant Switching Frequency: 300kHz}
n _{Programmable Soft-Start}
n _{Output Voltage Tracking}
n _{Available in 16-Pin 5mm × 3mm DFN}
APPLICATIONS
n _{Notebook and Palmtop Computers, PDA}
n _{Portable Instruments}
n _{Distributed Power Systems}
The LT^®3740 is a synchronous step-down switching
regulator controller that drives N-channel power MOSFET
stages. The controller uses valley current mode architecture
to achieve very low duty cycles with excellent transient
response without requiring a sense resistor.
The LT3740 includes an internal step-up converter to
provide a bias 7.8V higher than the input voltage for the
drive. This enables the part to work from an input voltage
as low as 2.2V.
The XREF pin is an external reference input that allows the
user to override the internal 0.8V feedback reference with
any lower value, allowing full control of the output voltage
during operation, output voltage tracking or soft-start.
The LT3740 has three current limit levels that can be
chosen by connecting the RANGE pin to ground, open,
and input respectively.
L, LT, LTC and LTM are registered trademarks of Linear Technology Corporation.
No R_SENSE is a trademark of Linear Technology Corporation. All other trademarks are the
property of their respective owners.
TYPICAL APPLICATION
High Efficiency Step-Down Converter
22μH
15k
0.22μF
LT3740
1μF
SWB
BGDP
V_IN
SHDN
XREF
BIAS
TGATE
SW
SN⁺
BGATE
1Ω
1Ω
1Ω
M1
HAT2168H
M2
HAT2165H
15k
V_C
20k
SN^–
PGND
1nF
RANGE GND FB
22pF
V_IN
3V to 12V
10μF
0.9μH
D1
B320A
39pF
V_OUT
1.8V
10A
100μF
s3
105k
80.6k
3740 TA01a
Efficiency vs Load Current
94
92
90 ^{VIN = 3V}
V_IN = 5V
88
86
V_IN = 12V
84
82
80
0
V_OUT = 1.8V
2
4
6
8
10
LOAD CURRENT (A)
3740 TA01b
3740fc
1