LX1681/1682
V
O LTA G E
- M
O D E
P W M C
O N T R O L L E R S
T
H E
I
N F I N I T E
P
O W E R
O F
I
N N O VA T I O N
P
R O D U C T I O N
D
A T A
S
H E E T
DESCRIPTION
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 mini-
mal external components.
The LX1681 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 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. 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.
K E Y F E AT U R E S
s
Fixed 200kHz Switching Frequency
s
Constant Frequency Voltage-Mode Control
Requires NO External Compensation
s
Hiccup-Mode Over-Current Protection
s
High Efficiency
s
Output Voltage Set By Resistor Divider
s
Under-Voltage Lockout
s
Soft-Start And Enable
s
Synchronous Rectification (LX1682)
s
Non-Synchronous Rectification (LX1681)
s
Small, 8-pin Surface Mount Package
A P P L I C AT I O N S
s
5V to 3.3V Or Less Buck Regulators
s
FPGA Supplies
s
Microprocessor Chipset Supplies
(e.g. Camino, Whitney, etc.)
s
Rambus
®
RIMM
TM
Supplies
s
Hard Disk Drives
s
Computer Add-on Cards
NOTE:
For current data & package dimensions, visit our web site:
http://www.linfinity.com.
PRODUCT HIGHLIGHT
V
BOOST
12V
C
3
1µF
1
V
IN
5V
C
1
1500µFx3
1
V
BOOST
12V
C
3
1µF
V
FB
SS
V
CC
CS
8
V
IN
5V
C
1
1500µFx2
C
SS
2
V
FB
SS
V
CC
CS
8
C
SS
7
2
7
0.1µF
3
4
LX1681
N.C.
GND
V
C1
TDRV
6
0.1µF
LX1682
3
Q
1
IRL3103S
L
1
5µH
R
SET
C
2
1500µF
x3
V
OUT
R
1
GND
BDRV
V
C1
TDRV
6
Q
1
IRL3103S
L
1
5µH
R
SET
C
2
1500µF
x3
V
OUT
R
1
5
4
5
D
2
MBR2545
R
2
Q
2
IRL3103S
R
2
LX1681 N
ON
-S
YNCHRONOUS
C
ONTROLLER
LX1682 S
YNCHRONOUS
C
ONTROLLER
PA C K A G E O R D E R I N F O R M A T I O N
T
A
(°C)
0 to 70
Output
Non-Synchronous
Synchronous
DM
Plastic SOIC
8-pin
LX1681CDM
LX1682CDM
Note: All surface-mount packages are available in Tape & Reel,
append the letter "T" to part number. (i.e. LX1681CDMT)
Copyright © 1999
Rev. 1.0 5/99
L
IN
F
INITY
M
ICROELECTRONICS
I
NC
.
11861 W
ESTERN
A
VENUE
, G
ARDEN
G
ROVE
, CA. 92841, 714-898-8121, F
AX
: 714-893-2570
1
MICROSEMI [ MICROSEMI CORPORATION ]
