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LX1669 Schematic ( PDF Datasheet ) - Microsemi Corporation

Teilenummer LX1669
Beschreibung PROGRAMMABLE DC : DC CONTROLLER
Hersteller Microsemi Corporation
Logo Microsemi Corporation Logo 




Gesamt 14 Seiten
LX1669 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 #: 1669
LX1669
PROGRAMMABLE DC:DC CONTROLLER
PR O D U C T I O N D ATA S H E E T
DESCRIPTION
The LX1669 is a Monolithic Switching
Regulator Controller IC 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. It provides
a programmable switching regulator out-
put suitable for powering Pentium® II and
other processors.
Programmable Synchronous Recti-
fier 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 soft-
ware. 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 effi-
ciencies of 85 – 90%, even with loads in
excess of 10A.
Short-circuit Current Limiting with-
out Expensive Current Sense Resis-
tors. 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 LX1669 is
available in an economical 16-pin narrow
body SOIC package.
NOTE: For current data & package dimensions, visit our web site: http://www.linfinity.com.
KEY FEATURES
s 5-Bit Programmable Output For CPU Core
Supply
s 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 Can Drive SCR Crowbar Or
Turn Off Signal Silver-Box Power Supply
s Digital-Compatible Inputs (Including VID Pins)
A P P L I C AT I O N S
s Socket 7 Processor Supplies
s Pentium II Processor Supplies
s Deschutes CPU & L2-Cache Memory
Supplies
s Voltage Regulator Modules
s General Purpose And Microprocessor
DC:DC Supplies
5V 12V
C8 C3
1µF 1µF
R3
10k
PWRGD
PRODUCT HIGHLIGHT
1 TDRV
2 VCC12
3 VCC5
4 PWRGD
5 OVP
6 VID0
7 VID1
8 VID2
L2, 1µH
Q1
IRL3102
PGND 16
BDRV 15
AGND
SS/EN
14
13
CSS
VFB 12 0.1µF
VCORE 11
VID4 10
VID3 9
VID4
VID3
VID2
VID1
VID0
C2
1500µFx3
L1 RSENSE
2.5µH 2.5m
Q2
IRL3303
Q4*
SCR
2N6504
CPU Core
VCORE
C1
1500µF x 6
PACKAGE ORDER INFO
* Q4 optional OVP crowbar
TA (°C)
D
Plastic SOIC
16-pin
0 to 70
LX1669CD
Note: All surface-mount packages are available in Tape & Reel, append the letter "T" to part number. (i.e. LX1669CDT)
Copyright © 1999
Rev. 1.0 4/99
LINFINITY MICROELECTRONICS INC.
11861 WESTERN AVENUE, GARDEN GROVE, CA. 92841, 714-898-8121, FAX: 714-893-2570
1






LX1669 Datasheet, Funktion
PRODUCT DATABOOK 1996/1997
LX1669
PROGRAMMABLE DC:DC CONTROLLER
PRODUCTION DATA SHEET
Pin
Number
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
Pin
Designator
TDRV
VCC12
VCC5
PWRGD
OVP
VID0
VID1
VID2
VID3
VID4
VCORE
VFB
SS/ENABLE
AGND
BDRV
PGND
FUNCTIONAL PIN DESCRIPTION
Description
Gate drive to the top FET.
+12V supply for the gate drivers. If 12V is not available in the application, a bootstrap circuit is required
to create the biasing voltage for the FET gate drivers.
+5V supply for internal biasing and power to the IC.
Open collector output, pulled down when the core voltage is not within ±10% of the DAC output.
Over-voltage protection: this pin is pulled to above 3V when the switcher output is above 17% of its set
voltage. This pin is capable of sourcing 40mA current, and can be used to drive an SCR crowbar or as a
signal to turn off the main power supply.
Input pins to the DAC. The output of the DAC sets the nominal voltage of the PWM output (see Table 1).
These inputs are TTL-compatible.
Output (CPU core) voltage, connected to the output of the regulator (after the sense resistor). This pin is
also connected to the power good and the over current comparators in the IC.
Dual function pin for feedback and current sensing. The peak voltage of this is set 40mV above the
nominal set-point (VID)
60mV, the over current
voltage. When
comparator will
the
be
voltage difference
tripped. The over
between this pin and
current tripping level
cVaOnUTb(epsinet1a5s)
exceeds
I = 60mV/RSENSE where RSENSE is the sensing resistance (see Application Note section).
Soft-startup and hiccup capacitor pin. During startup, the voltage of this pin controls the core voltage. An
internal 20kresistor and the external capacitor set the time constant for the soft-startup. Soft-start does
not begin until the supply voltage exceeds the UVLO threshold. When over-current occurs, this capacitor is
used for timing the hiccup. See Application Information for more detail. The PWM output can be disabled
by pulling the SS/ENABLE pin below 0.5V.
Analog ground.
Bottom FET drive.
Power ground. Ground return for FET drivers.
6 Copyright © 1999
Rev. 1.0 4/99

6 Page









LX1669 pdf, datenblatt
PRODUCT DATABOOK 1996/1997
LX1669
PROGRAMMABLE DC:DC CONTROLLER
PRODUCTION DATA SHEET
APPLICATION INFORMATION
CURRENT LIMIT (continued)
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.
PCB Sense Resistor
A PCB sense resistor should be constructed as shown in Figure 7.
By attaching directly to the large pads for the capacitor and
inductor, heat is dissipated efficiently by the larger copper masses.
Connect the current sense lines as shown to avoid any errors.
Inductor
2.5mSense Resistor
100mil Wide, 850mil Long
2.5mm x 22mm (2 oz/ft2 copper)
Output
Capacitor Pad
L RL
Load
RS
Current
Sense
Comparator
CS
VCS RS2
FIGURE 8 — Current Sense Circuit
The voltage across the capacitor will be equal to the current
flowing through the resistor, i.e.
VCS = ILRL
Since VCS reflects the inductor current, by selecting the
appropriate RS and CS, VCS can used to sense current.
Design Example
(Pentium II circuit, with a maximum static current of 14.2A)
The gain of the sensor can be characterized as:
Sense Lines
|T(jω)|
FIGURE 7 — Sense Resistor Construction Diagram
Recommended sense resistor sizes are given in the following
table:
TABLE 3 - PCB Sense Resistor Selection Guide
Copper Copper Desired Resistor
Weight Thickness
Value
Dimensions (w x l)
mm inches
2 oz/ft2 68µm
2.5m
5m
2.5 x 22
2.5 x 43
0.1 x 0.85
0.1 x 1.7
Loss-Less Current Sensing Using Resistance of Inductor
Any inductor has a parasitic resistance (RL) which causes a DC
voltage drop when current flows through the inductor. Figure 8
shows a sensor circuit comprising of a surface mount resistor, RS,
and capacitor, CS, in parallel with the inductor, eliminating the
current sense resistor.
The current flowing through the inductor is a triangle wave. If
the sensor components are selected such that:
L/RL = RS * CS
RL
L/RSCS
1/RSCS RL/L
ω
FIGURE 9 — Sensor Gain
The dc/static tripping current Itrip,S satisfies:
Itrip,S =
Vtrip
RL
Select L/RSCS RL to have higher dynamic tripping current than
the static one. The dynamic tripping current Itrip,d satisfies:
Itrip,d =
Vtrip
L/(RSCS )
12 Copyright © 1999
Rev. 1.0 4/99

12 Page





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