LX1681/1682
TM
®
Voltage-Mode PWM Controllers
P
RODUCTION
D
ATA
S
HEET
DESCRIPTION
KEY FEATURES
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Microsemi
.C
OM
The LX1681/1682 are monolithic,
pulse-width modulator controller ICs.
They are designed to implement a
flexible, low cost buck (step-down)
regulator supply with minimal external
components.
The LX1681 is a non-synchronous
controller;
the
LX1682
has
a
synchronous driver for higher efficiency.
The output voltage is adjustable by
means of a resistor divider to set the
voltage between 1.25V and 4.5V.
Short-circuit current limiting can be
implemented without expensive current
sense resistors. Current is sensed using
the voltage drop across the R
DS(ON)
of the
MOSFET — sensing is delayed for 1µs
to eliminate MOSFET ringing errors.
Hiccup-mode fault protection reduces
average power to the power elements
during short-circuit conditions.
Switching frequency is fixed at
200kHz for optimal cost and space.
Under-voltage lockout and soft-start
for optimal start-up performance. Pulling
the soft-start pin to ground can disable
the LX1681/82.
Small 8-pin SOIC packaging reduces
board space. Optimized for 5V-to-3.3V
or
5V-to-2.5V
conversion,
the
LX1681/82 can also be used for
converting 12V to 5V, 3.3V or other
voltages
with
high
efficiency,
eliminating the need for bulky heat sinks.
Fixed 200kHz Switching Frequency
Constant Frequency Voltage-Mode
Control Requires NO External
Compensation
Hiccup-Mode Over-Current
Protection
High Efficiency
Output Voltage Set By Resistor
Divider
Under-Voltage Lockout
Soft-Start And Enable
Synchronous Rectification
(LX1682)
Non-Synchronous Rectification
(LX1681)
Small, 8-pin Surface Mount
Package
APPLICATIONS
5V to 3.3V Or Less Buck
Regulators
FPGA Supplies
Microprocessor Chipset Supplies
(e.g. Camino, Whitney, etc.)
©
Rambus RIMM™ Supplies
Hard Disk Drives
Computer Add-on Cards
IMPORTANT:
For the most current data, consult
MICROSEMI’s
website:
http://www.microsemi.com
PRODUCT HIGHLIGHT
V
BO OST
12V
V
IN
5V
C
3
1µF
C
1
1500µF
x3
C
3
1µF
V
BOO ST
12V
V
IN
5V
C
1
V
FB
C
SS
0.1µF
V
C2
CS
V
FB
C
SS
V
C2
CS
1500µF
x3
SS
SS
LX1681
N.C.
GND
V
C1
TDRV
R
SET
D
2
Q
1
IRL3103S
L
1
5µH
C
2
1500µF
x3
R
1
0.1µF
V
OU T
LX1682
G ND
BDRV
V
C1
TDRV
R
SET
Q
1
IRL3103S
L
1
5µH
C
2
1500µF
x3
R
1
V
OU T
R
2
MBR2545
R
2
Q
2
IRL3103S
LX1681/1682
LX1681/1682
LX1681 Non-Synchronous Controller
LX1682 Synchronous Controller
PACKAGE ORDER INFO
T
A
(°C)
0 to 70
O
UTPUT
Non-Synchronous
Synchronous
DM
Plastic SOIC
8-PIN
LX1681CDM
LX1682CDM
RoHS Compliant / Pb-free
Transition D/C: 0440
Note: Available in Tape & Reel. Append the letters “TR” to the part number. (i.e. LX1681CDM-TR)
Copyright
©
2000
Rev. 1.1b,2005-03-09
Microsemi
Linfinity Microelectronics Division
11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570
Page 1
MICROSEMI [ MICROSEMI CORPORATION ]
