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LX1665ACDW Schematic ( PDF Datasheet ) - Microsemi Corporation

Teilenummer LX1665ACDW
Beschreibung DUAL OUTPUT PWM CONTROLLERS WITH 5-BIT DAC
Hersteller Microsemi Corporation
Logo Microsemi Corporation Logo 




Gesamt 17 Seiten
LX1665ACDW 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
LX1664/64A, LX1665/65A
DUAL OUTPUT PWM CONTROLLERS WITH 5-BIT DAC
PRODUCTION DATA SHEET
DESCRIPTION
The LX1664/64A and LX1665/65A 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 LX1664A and
LX1665A have reduced current sense com-
parator threshold for optimum perfor-
mance using a sense resistor. For applica-
tions 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).
Linear Regulator Driver. The LX1664/
65 family of devices have a secondary
regulator output. This can drive a MOSFET
or bipolar transistor as a pass element to
construct a low-cost adjustable linear regu-
lator suitable for powering a 1.5V GTL+ bus
or 2.5V clock supply.
(continued next page)
IMPORTANT: For the most current data, consult LinFinity's web site: http://www.linfinity.com.
KEY FEATURES
I 5-bit Programmable Output For CPU Core
Supply
I Adjustable Linear Regulator Driver Output
I No Sense Resistor Required For Short-
Circuit Current Limiting
I Designed To Drive Either Synchronous Or
Non-Synchronous Output Stages
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
(LX1665 only)
A P P L I C AT I O N S
I Socket 7 (Pentium Class) 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
PRODUCT HIGHLIGHT
LX1665 IN A PENTIUM II SINGLE-CHIP POWER SUPPLY SOLUTION
C3
0.1µF
VID0
VID1
VID2
VID3
VID4
12V
U1
LX1665
1 SS
2 INV
V3
CC_CORE
4 VID0
5 VID1
6 VID2
7 VID3
8 VID4
9 LFB
VC1 18
TDRV 17
GND 16
BDRV 15
VCC 14
CT 13
OV 12
LDRV 11
PWRGD 10
18-pin
Wide-Body SOIC
F1 20A
5V
L2
1µH
C5
1µF
Q1
IRL3102
Q2
IRL3303
6.3V
1500µF x3
C2
L1
2.5µH
R1
0.0025
Supply Voltage
for CPU Core
VOUT
C1
6.3V, 1500µF x 3**
C8
680pF
Q4
IRLZ44
C9
330µF
** Three capacitors for Pentium
Four capacitors for Pentium II
Supply Voltage
For I/O Chipset or GTL+ Bus
R5 C7
OV 330µF
PWRGD
R6
TA (°C)
PACKAGE ORDER INFORMATION
N
Plastic DIP
16-pin
N
Plastic DIP
18-pin
D
Plastic SOIC
16-pin
DW
Plastic
18-pin
SOIC
Wide
0 to 70
LX1664CN
LX1665CN
LX1664CD
LX1665CDW
LX1664ACN
LX1665ACN
LX1664ACD
LX1665ACDW
Note: All surface-mount packages are available in Tape & Reel. Append the letter "T" to part number. (e.g. LX1664CDT)
Copyright © 1999
Rev. 1.2 11/99
LINFINITY MICROELECTRONICS INC.
11861 WESTERN AVENUE, GARDEN GROVE, CA. 92841, 714-898-8121, FAX: 714-893-2570
1






LX1665ACDW Datasheet, Funktion
PRODUCT DATABOOK 1996/1997
LX1664/64A, LX1665/65A
DUAL OUTPUT PWM CONTROLLERS WITH 5-BIT DAC
PRODUCTION DATA SHEET
BLOCK DIAGRAM
SS 1
INV 2
VCC_CORE 3
CT 13
40mV
100mV **
VCC
2V Out
UVLO
10.6/10.1
Trimmed
2V REF
Internal
VCC
VREG
Error Comp
CS Comp
Off-Time
Controller
PWM Latch
SQ
R DOM R Q
Break
Before
Make
SYNC EN
Comp
OV Comp
0.7V
UV Comp
18 VC1
17 TDRV
16 GND
15 BDRV
14 VCC
12 OV*
10 PWRGD*
10k
DAC OUT
DAC
1.5V
Linear Op Amp
LX1665/1665A ONLY
11 LDRV
4
VID0
5
VID1
6
VID2
7
VID3
8
VID4
9 LFB
Note: Pin numbers are correct for LX1665/1665A, 18-pin package.
* Not connected on LX1664/1664A.
** 60mV in LX1664A/1665A.
FIGURE 5 LX1664/1665 Block Diagram
6 Copyright © 1999
Rev. 1.2 11/99

6 Page









LX1665ACDW pdf, datenblatt
PRODUCT DATABOOK 1996/1997
LX1664/64A, LX1665/65A
DUAL OUTPUT PWM CONTROLLERS WITH 5-BIT DAC
PRODUCTION DATA SHEET
USING THE LX1664/65 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
VOUT
fS * LOUT * 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 LX1664 & 1665 have a threshold of 100mV, while the LX1664A
and LX1665A 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 LX1664/65 and 60mV for LX1664A/65A) 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
LX1664 or LX1665
LX1664A or LX1665A
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. 1.2 11/99

12 Page





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