LX1681/ 1682
V OLTAGE- MODE PWM CONTROLLERS
T H E I N F I N I T E P O W E R O F I N N O V A T I O N
P R O D U C T I O N D A T A S H E E T
D E S C R I P T I O N
K E Y F E A T U R E S
■ Fixed 200kHz Switching Frequency
The LX1 681 /1 682 are monolithic, pulse-
width modulator controller ICs. They are
designed to implement a flexible, low cost
buck (step-down) regulator supply with mini-
mal external components.
Hiccup-mode fault protection reduces
average power to the power elements during
short-circuit conditions.
Switchingfrequency is fixed at 200kHz
for optimal cost and space.
■ Constant Frequency Voltage-Mode Control
Requires NO External Compensation
■ Hiccup-Mode Over-Current Protection
■ High Efficiency
The LX1 681 is a non-synchronous con-
troller; 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 RDS(ON) of the MOSFET
— sensing is delayed for 1µs to eliminate
MOSFET ringing errors.
Under-voltage lockout and soft-start
for optimal start-up performance. The
LX1681/82 can be disabled by pulling the soft-
start pin to ground.
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.
■ 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
A P P L I C A T I O N S
■ 5V to 3.3V Or Less Buck Regulators
■ FPGA Supplies
■ Microprocessor Chipset Supplies
NOTE: For current data & package dimensions, visit our web site: http://www.linfinity.com.
(e.g. Camino, Whitney, etc.)
■ Rambus® RIMMTM Supplies
■ Hard Disk Drives
■ Computer Add-on Cards
P R O D U C T H I G H L I G H T
VBOOST
12V
V
IN
VBOOST
12V
V
IN
5V
5V
C3
1µF
C1
C3
1µF
C1
1500µFx2
1500µFx3
1
2
3
4
8
1
2
8
VFB
VCC
CS
VFB
VCC
CS
CSS
CSS
7
6
5
7
6
5
SS
SS
LX1682
0.1µF
LX1681
0.1µF
Q1
IRL3103S
VOUT
Q1
IRL3103S
GND
BDRV
VC1
3
4
VOUT
N.C.
GND
VC1
C2
L
5µH
C2
1
L
5µH
TDRV
R
1
1
TDRV
R
1
1500µF
x3
1500µF
x3
R
SET
R
SET
D2
Q2
R
R
2
MBR2545
2
IRL3103S
LX1681 NON-SYNCHRONOUS CONTROLLER
LX1682 SYNCHRONOUS CONTROLLER
P A C K A G E O R D E R I N F O R M A T I O N
Plastic SOIC
T (°C)
Output
DM
8-pin
A
Non-Synchronous
Synchronous
LX1681CDM
0 to 70
LX1682CDM
Note: All surface-mount packages are available in Tape & Reel,
append the letter "T" to part number. (i.e. LX1681CDMT)
L I N F I N I T Y M I C R O E L E C T R O N I C S I N C .
11861 WESTERN AVENUE, GARDEN GROVE, CA. 92841, 714-898-8121, FAX: 714-893-2570
Copyright © 1999
Rev. 1.0 5/ 99
1
MICROSEMI [ Microsemi ]
