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LX1662ACN Schematic ( PDF Datasheet ) - Microsemi Corporation

Teilenummer LX1662ACN
Beschreibung SINGLE-CHIP PROGRAMMABLE PWM CONTROLLERS WITH 5-BIT DAC
Hersteller Microsemi Corporation
Logo Microsemi Corporation Logo 




Gesamt 15 Seiten
LX1662ACN Datasheet, Funktion
T H E I N F I N I T E P O W E R O F I N N O VAT I O N
L I N D O C # : 1662
LX1662/62A, LX1663/63A
SINGLE-CHIP PROGRAMMABLE PWM CONTROLLERS WITH 5-BIT DAC
PRODUCTION DATA SHEET
DESCRIPTION
The LX1662/62A and LX1663/63A are
Monolithic Switching Regulator Con-
troller IC’s designed to provide 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.
Short-Circuit Current Limiting with-
out Expensive Current Sense Resistors.
Current-sensing mechanism can use PCB
trace resistance or the parasitic resistance of
the main inductor. The LX1662A and
LX1663A have reduced current sense com-
parator threshold for optimum perfor-
mance using a PCB trace. For applications
requiring a high degree of accuracy, a
conventional sense resistor can be used to
sense current.
Programmable Synchronous Recti-
fier Driver for CPU Core. The main
output is adjustable from 1.3V to 3.5V using
a 5-bit code. The IC can read a VID signal
set by a DIP switch on the motherboard, or
hardwired into the processor’s package (as
in the case of Pentium® Pro and Pentium II
processors). 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, conforming to the
Intel Corporation specification. The device
can drive dual MOSFET’s resulting in typical
efficiencies of 85 - 90% even with loads in
excess of 10 amperes. For cost sensitive
applications, the bottom MOSFET can be
replaced with a Schottky diode (non-syn-
chronous operation).
Smallest Package Size. The LX1662 is
available in a narrow body 14-pin surface
mount IC package for space sensitive appli-
cations. The LX1663 provides the additional
functions of Over Voltage Protection (OVP)
and Power Good (PWRGD) output drives
for applications requiring output voltage
monitoring and protection functions.
Ultra-Fast Transient Response Re-
duces System Cost. The modulated off-
time architecture results in the fastest tran-
sient response for a given inductor, reduc-
ing output capacitor requirements, and re-
ducing the total regulator system cost.
Over-Voltage Protection and Power
Good Flag. The OVP output in the LX1663
& LX1663A can be used to drive an SCR
crowbar circuit to protect the load in the
event of a short-circuit of the main MOSFET.
The LX1663 & LX1663A also have a logic-
level Power Good Flag to signal when the
output voltage is out of specified limits.
IMPORTANT: For the most current data, consult LinFinity's web site: http://www.linfinity.com.
PRODUCT HIGHLIGHT
KEY FEATURES
I 5-bit Programmable Output For CPU Core
Supply
I No Sense Resistor Required For Short-
Circuit Current Limiting
I Designed To Drive Either Synchronous Or
Non-Synchronous Output Stages
I Lowest System Cost Possible For Price-
Sensitive Pentium And Pentium II Class
Applications
I Soft-Start Capability
I Modulated, Constant Off-Time Architecture
For Fast Transient Response And Simple
System Design
I Available Over-Voltage Protection (OVP)
Crowbar Driver And Power Good Flag
(LX1663 only)
I Small, Surface-Mount Packages
A P P L I C AT I O N S
I Socket 7 Microprocessor Supplies
(including Intel Pentium Processor, AMD-
K6TM And Cyrix® 6x86TM, Gx86TM and M2TM
Processors)
I Pentium II and Deschutes Processor & L2-
Cache Supplies
I Voltage Regulator Modules
I General Purpose DC:DC Converter
Applications
LX1662
IN A PENTIUM/PENTIUM II
SINGLE-CHIP POWER
SUPPLY SOLUTION
C3
0.1µF
VID0
VID1
VID2
VID3
VID4
12V 5V
U1
LX1662
1 SS
2 INV
V3
CC_CORE
4 VID0
5 VID1
6 VID2
7 VID3
VC1 14
TDRV 13
GND 12
BDRV 11
VCC 10
CT 9
VID4 8
14-pin, Narrow Body SOIC
L2
1µH
C5
1µF
Q1
IRL3102
6.3V
1500µF x3
C2
C8
680pF
L1, 2.5µH
R1
Q2
IRL3303
2.5m9
6.3V, 1500µF x 3**
** Three capacitors for Pentium
Four capacitors for Pentium II
Supply Voltage VOUT
for CPU Core
C1
TA (°C)
PACKAGE ORDER INFORMATION
N
Plastic DIP
14-pin
N
Plastic DIP
16-pin
D
Plastic SOIC
14-pin
D
Plastic SOIC
16-pin
0 to 70
LX1662CN
LX1662ACN
LX1663CN
LX1663ACN
LX1662CD
LX1662ACD
LX1663CD
LX1663ACD
Note: All surface-mount packages are available in Tape & Reel. Append the letter "T" to part number. (i.e. LX1662CDT)
Copyright © 1999
Rev. 1.1 11/99
LINFINITY MICROELECTRONICS INC.
11861 WESTERN AVENUE, GARDEN GROVE, CA. 92841, 714-898-8121, FAX: 714-893-2570
1






LX1662ACN Datasheet, Funktion
PRODUCT DATABOOK 1996/1997
LX1662/62A, LX1663/63A
SINGLE-CHIP PROGRAMMABLE PWM CONTROLLERS WITH 5-BIT DAC
PRODUCTION DATA SHEET
BLOCK DIAGRAM
SS 1
INV 2
VCC_CORE 3
CT 11
40mV
100mV **
VCC
2V Out
UVLO
10.6/10.1
Trimmed
2V REF
Internal
VCC
VREG
OV
Error Comp
CS Comp
Off-Time
Controller
PWM Latch
SQ
R DOM R Q
Break
Before
Make
SYNC EN
Comp
OV Comp
0.7V
10k
D OUT
UV Comp
16 VC1
15 TDRV
14 GND
13 BDRV
12 VCC
10 OV*
9 PWRGD*
DAC
4
VID0
5
VID1
6
VID2
7
VID3
8
VID4
LX1663/1663A ONLY
Note: Pin numbers are correct for LX1663/1663A, 16-pin package.
* Not connected on the LX1662/1662A.
** 60mV in LX1662A & LX1663A
FIGURE 5 Block Diagram
6 Copyright © 1999
Rev. 1.1 11/99

6 Page









LX1662ACN pdf, datenblatt
PRODUCT DATABOOK 1996/1997
LX1662/62A, LX1663/63A
SINGLE-CHIP PROGRAMMABLE PWM CONTROLLERS WITH 5-BIT DAC
PRODUCTION DATA SHEET
USING THE LX1662/63 DEVICES
INPUT INDUCTOR SELECTION
In order to cope with faster transient load changes, a smaller
output inductor is needed. However, reducing the size of the
output inductor will result in a higher ripple voltage on the input
supply. This noise on the 5V rail can affect other loads, such as
graphics cards. It is recommended that a smaller input inductor,
L2 (1 - 1.5µH), is used on the 5V rail to filter out the ripple. Ensure
that this inductor has the same current rating as the output
inductor.
C1 FILTER CAPACITOR SELECTION (continued)
aluminum electrolytic, and have demonstrated reliability. The
Oscon series from Sanyo generally provides the very best
performance in terms of long term ESR stability and general
reliability, but at a substantial cost penalty. The MV-GX series
provides excellent ESR performance, meeting all Intel transient
specifications, at a reasonable cost. Beware of off-brand, very-low
cost filter capacitors, which have been shown to degrade in both
ESR and general electrolyte characteristics over time.
C1 FILTER CAPACITOR SELECTION
The capacitors on the output of the PWM section are used to filter
the output current ripple, as well as help during transient load
conditions, and the capacitor bank should be sized to meet ripple
and transient performance specifications.
When a transient (step) load current change occurs, the output
voltage will have a step which equals the product of the Effective
Series Resistance (ESR) of the capacitor and the current step (I).
when current increases from low (in sleep mode) to high, the
output voltage will drop below its steady state value. In the
advanced microprocessor power supply, the capacitor should
usually be selected on the basis of its ESR value, rather than the
capacitance or RMS current capability. Capacitors that satisfy the
ESR requirement usually have a larger capacitance and current
capability than needed for the application. The allowable ESR can
be found by:
ESR * (IRIPPLE + I) < VEX
Where VEX is the allowable output voltage excursion in the
transient and IRIPPLE is the inductor ripple current. Regulators such
as the LX166x series, have adaptive output voltage positioning,
which adds 40mV to the DC set-point voltage — VEX is therefore
the difference between the low load voltage and the minimum
dynamic voltage allowed for the microprocessor.
Ripple current is a function of the output inductor value (LOUT),
and can be approximated as follows:
IRIPPLE =
VIN - VOUT
fS * LOUT
*
VOUT
VIN
Where fS is the switching frequency.
Electrolytic capacitors can be used for the output filter capaci-
tor bank, but are less stable with age than tantalum capacitors. As
they age, their ESR degrades, reducing the system performance
and increasing the risk of failure. It is recommended that multiple
parallel capacitors are used so that, as ESR increases with age,
overall performance will still meet the processor's requirements.
There is frequently strong pressure to use the least expensive
components possible, however, this could lead to degraded long-
term reliability, especially in the case of filter capacitors. Linfinity's
demo boards use Sanyo MV-GX filter capacitors, which are
CURRENT LIMIT
Current limiting occurs when a sensed voltage, proportional to
load current, exceeds the current-sense comparator threshold
value. The current can be sensed either by using a fixed sense
resistor in series with the inductor to cause a voltage drop
proportional to current, or by using a resistor and capacitor in
parallel with the inductor to sense the voltage drop across the
parasitic resistance of the inductor.
The LX166x family offers two different comparator thresholds.
The LX1662 & 1663 have a threshold of 100mV, while the LX1662A
and LX1663A have a threshold of 60mV. The 60mV threshold is
better suited to higher current loads, such as a Pentium II or
Deschutes processor.
Sense Resistor
The current sense resistor, R1, is selected according to the formula:
R1 = VTRIP / ITRIP
Where VTRIP is the current sense comparator threshold (100mV
for LX1662/63 and 60mV for LX1662A/63A) and ITRIPis the desired
current limit. Typical choices are shown below.
TABLE 2 - Current Sense Resistor Selection Guide
Load
Sense Resistor Recommended
Value
Controller
Pentium-Class Processor (<10A)
Pentium II Class (>10A)
5m
2.5m
LX1662 or LX1663
LX1662A or LX1663A
A smaller sense resistor will result in lower heat dissipation (I²R)
and also a smaller output voltage droop at higher currents.
There are several alternative types of sense resistor. The
surface-mount metal “staple” form of resistor has the advantage of
exposure to free air to dissipate heat and its value can be
controlled very tightly. Its main drawback, however, is cost. An
alternative is to construct the sense resistor using a copper PCB
trace. Although the resistance cannot be controlled as tightly, the
PCB trace is very low cost.
12 Copyright © 1999
Rev. 1.1 11/99

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