LT1765/LT1765-1.8/LT1765-2.5/
LT1765-3.3/LT1765-5
Monolithic 3A, 1.25MHz
Step-Down Switching Regulator
FEATURES
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DESCRIPTION
The LT
®
1765 is a 1.25MHz monolithic buck switching
regulator. A high efficiency 3A, 0.09Ω switch is included
on the die together with all the control circuitry required
to construct a high frequency, current mode switching
regulator. Current mode control provides fast transient
response and excellent loop stability.
New design techniques achieve high efficiency at high
switching frequencies over a wide operating voltage
range. A low dropout internal regulator maintains con-
sistent performance over a wide range of inputs from
24V systems to Li-Ion batteries. An operating supply
current of 1mA improves efficiency, especially at lower
output currents. Shutdown reduces quiescent current to
15μA. Maximum switch current remains constant at all
duty cycles. Synchronization allows an external logic level
signal to increase the internal oscillator into the range of
1.6MHz to 2MHz.
Full cycle-by-cycle current control and thermal shutdown
are provided. High frequency operation allows the reduc-
tion of input and output filtering components and permits
the use of chip inductors.
L,
LT, LTC and LTM are registered trademarks of Linear Technology Corporation.
*Patent Pending
3A Switch in a Thermally Enhanced 16-Lead
TSSOP or 8-Lead SO Package
Constant 1.25MHz Switching Frequency
Wide Operating Voltage Range: 3V to 25V
High Efficiency 0.09Ω Switch
1.2V Feedback Reference Voltage
Uses Low Profile Surface Mount Components
Low Shutdown Current: 15μA
Synchronizable to 2MHz
Current Mode Loop Control
Constant Maximum Switch Current Rating at
All Duty Cycles*
Available in 8-Lead SO and 16-Lead Thermally
Enhanced TSSOP Packages
APPLICATIONS
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DSL Modems
Portable Computers
Regulated Wall Adapters
Battery-Powered Systems
Distributed Power
TYPICAL APPLICATION
5V to 3.3V Step-Down Converter
CMDSH-3
0.18μF
85
V
IN
LT1765-3.3
OFF ON
SHDN
SYNC
FB
GND
V
C
2.2nF
UPS120
4.7μF
CERAMIC
V
SW
EFFICIENCY (%)
INPUT
5V
2.2μF
CERAMIC
BOOST
1.5μH
OUTPUT
3.3V
2.5A
90
Efficiency vs Load Current
V
IN
= 10V
V
OUT
= 5V
80
75
1765 TA01
70
0
1.0
1.5
0.5
SWITCH CURRENT (A)
2.0
1765 • TAO1a
1765fd
1
LINER [ LINEAR TECHNOLOGY ]
