LIN D
O C
#:
1668
LX1668
P
ROGRAMMABLE
M
U LTIPLE
O
UTPUT
DC:DC C
ONTROLLER
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 LX1668 is a Monolithic Switching
Regulator Controller IC
designed to pro-
vide a low cost, high performance adjustable
power supply for advanced microprocessors
and other applications requiring a very fast
transient response and a high degree of
accuracy. It provides a programmable
switching regulator output, together with one
internal linear low dropout regulator and one
adjustable linear regulator driver. The LX1668
offers a triple-output single-chip power sup-
ply for Pentium
®
II and other processors.
Programmable Synchronous Rectifier
Driver for CPU Core.
The main output is
adjustable from 1.3 to 3.5V using a TTL-
compatible 5-bit digital code to meet Intel
specifications. The IC can read the signal
from a DIP-switch, hardwired to Pentium II
processor’s pins or from software. The 5-bit
code adjusts the output voltage between 1.30
and 2.05V in 50mV increments, and between
2.0 and 3.5V in 100mV increments. The
device can drive dual MOSFET’s resulting in
typical efficiencies of 85 – 90%, even with
loads in excess of 10A.
Internal Low Dropout [LDO] Regulator
provides a fixed 2.5V output for powering the
clock circuit at up to 250mA.
External Linear Regulator Driver
out-
put can be connected to a MOSFET to provide
a high-current adjustable LDO function suit-
able for supplying the GTL+ bus circuitry on
a Pentium II processor motherboard at 1.5V.
Short-circuit Current Limiting without
Expensive Current Sense Resistors.
The
current sensing mechanism can use a PCB
trace resistance or the parasitic resistance of
the main inductor. For applications requiring
a high degree of accuracy, a conventional
sense resistor can be used.
Ultra-Fast Transient Response Re-
duces System Cost.
The fixed frequency
modulated off-time architecture results in the
fastest transient response for a given inductor.
Small Package Size.
The LX1668 is available
in an economical 20-pin wide body SOIC or
a space-saving 20-pin TSSOP package.
K E Y F E AT U R E S
s
5-Bit Programmable Output For CPU Core
Supply
s
Internal Fixed 2.5V Low Dropout Regulator
s
Adjustable Linear Regulator Driver
s
Complete Single-Chip Power Solution For
Pentium II Processors
s
No Sense Resistor Required For Short-Circuit
Current Limiting
s
Soft-Start And Hiccup-Mode Current Limiting
Functions
s
Modulated Constant Off-Time Control
Mechanism For Fast Transient Response And
Simple System Design
s
Power Good Flag
s
Over-Voltage Pin & SCR
s
Digital-Compatible Inputs
(Including VID Pins)
s
Output Disable Function Shuts Off PWM While
Keeping 2.5V LDO Active - Compatible With
"Green PC" And "Instant On" Requirements
s
Compatible to VRM8.2 - 8.4 Specifications
A P P L I C AT I O N S
s
Pentium II & Pentium III Processor Supplies
s
Voltage Regulator Modules
s
General Purpose And Microprocessor DC:DC
Supplies
NOTE:
For current data & package dimensions, visit our web site:
http://www.linfinity.com.
PRODUCT HIGHLIGHT
5V
12V
C8
1µF
V
OUT2
2.5V
L2
1µH
C7
1µF
1
20
19
18
17
16
C
SS
15
14
13
12
11
C2
Q1
IRL3102
1500µFx3
C3
1µF
L1
2.5µH
Q2
IRL3303
R
SENSE
2.5mΩ
CPU Core
V
CORE
TDRV
V
CC12
V
CC5
V
OUT2
V
CC3
L
DRV
L
FB
VID0
VID1
VID2
PGND
BDRV
AGND
SS/EN
V
FB
V
CORE
OVP
VID4
VID3
C5
22µF
C9
1µF
2
3
4
3.3V
C4
330µF
V
OUT3
1.5V
5
6
7
0.1µF
LX1668
SCR
2N6504
Q4*
C1
1500µF x 6
Q3
IRLZ44
PWRGD
PWRGD
8
9
10
C6
330µF
R1, 0
R2, 50k
VID4
VID3
VID2
VID1
VID0
R3
10k
*
Q4 optional
OVP crowbar
3.3V / 5V
PA C K A G E O R D E R I N F O R M AT I O N
T
A
(°C)
0 to 70
DW
Plastic SOWB
20-pin
LX1668CDW
PW
Plastic TSSOP
20-pin
LX1668CPW
Note: All surface-mount packages are available in Tape & Reel, append the letter "T" to part number. (i.e. LX1668CPWT)
Copyright © 1999
Rev. 1.0 4/99
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
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