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PDF LX1671 Data sheet ( Hoja de datos )
| Número de pieza | LX1671 | |
| Descripción | Multiple Output LoadSHARE PWM | |
| Fabricantes | Microsemi Corporation | |
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INTEGRATED PRODUCTS
LX1671
Multiple Output LoadSHARE™ PWM
PRODUCTION DATA SHEET
DESCRIPTION
The LX1671 is a highly integrated The additional outputs are capable of
power supply controller IC featuring supplying up to 5A (Linear Regulator
www.tDharteaeShPeeWt4UM.netswitching regulator stages Driver) and 15A (Switching Regulator)
with an additional onboard linear for I/O, memory, termination, and other
regulator driver.
supplies surrounding today’s micro-
Two of the constant frequency processor designs.
voltage-mode PWM phases can be Each PWM regulator output is
easily configured for a single Bi-Phase programmed via a simple voltage-divider
high current output or two in- network. The LX1671, utilizing
dependently regulated outputs. Each MOSFET RDS(ON) impedance, monitors
phase incorporates a fully pro- current limit conditions, in each PWM
grammable soft-start sequence. This phase, without the use of expensive
versatility yields either three or four current sense resistors.
independently regulated outputs with The LX1671 was designed to give
full power sequencing capability giving design engineers maximum flexibility
system designers the ultimate with respect to the MOSFET supply.
flexibility in power supply design.
Each phase can utilize different supply
In Bi-Phase operation, the high voltages for efficient use of available
current (>30A) output can utilize supply rails. Additionally, when two
different supply rails allowing Forced phases are configured in Bi-Phase output,
Current Sharing† from different the LoadSHARETM topology can be
sources. Power loss and noise, due to programmed via inductor ESR selection.
the ESR of the input capacitors, are There are three other methods that can
minimized by operating each PWM also be used with LoadSHARETM. These
output 180° out of phase. This other methods are presented in the theory
architecture also minimizes capacitor of operation section of this data sheet.
requirements while maximizing re-
gulator response.
IMPORTANT: For the most current data, consult MICROSEMI’s website: http://www.microsemi.com
LoadSHARE is a Trademark of Microsemi Corporation
PRODUCT HIGHLIGHT
KEY FEATURES
Up to Four Independently
Regulated Outputs
Outputs As Low As 0.8V
Generated From An Internal 1%
Reference
Multiphase High Current Output
Reduces Required Capacitance
Integrated High Current MOSFET
Drivers
300kHz High Frequency Operation
Minimizes External Component
Requirements
Independent Phase Programmable
Soft-Start and Power Sequencing
Adjustable Linear Regulator Driver
Output
No current-sense resistors
DDR Termination Compliant
APPLICATIONS/BENEFITS
Multi-Output Power Supplies
Video Card Power Supplies
PC Peripherals
Portable PC Processor and I/O
Supply
Refer to Typical
Application for
com plete circuit.
DDR Term ination
....
Mem ory Core
12V
5V
LX1671
Core
Graphics
Controller
Mem ory Bus
DDR Mem ory
3.3V
I/O
Copyright © 2000
Rev. 1.0a, 2004-06-14
TA (°C)
0 to 70
PACKAGE ORDER INFO
Plastic TSSOP
Plastic MLPQ
PW 38-Pin
LQ 38-Pin
LX1671-CPW
LX1671-CLQ
Note: Available in Tape & Reel. Append the letters “TR” to the part number (i.e. LX1671CPWTR)
Microsemi
Integrated Products, Power Management
11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570
Page 1
1 page  
INTEGRATED PRODUCTS
LX1671
Multiple Output LoadSHARE™ PWM
PRODUCTION DATA SHEET
ELECTRICAL CHARACTERISTICS (CONTINUED)
Unless otherwise specified, the following specifications apply over the operating ambient temperature 0°C ≤ TA ≤ 70°C except where
otherwise noted and the following test conditions: VCC = 5V, VCCL = 5V, VCX = 12V , HOX = LOX = 3000pF Load.
Parameter
Symbol
Test Conditions
` UVLO AND SOFT-START (SS)
Start-Up Threshold (VCX VCCL )
Start-Up Threshold (VCC)
Hysteresis
(VCC)
SS Input Resistance
RSS
SS Shutdown Threshold
VSHDN
Hiccup Mode Duty Cycle
` LINEAR REGULATOR CONTROLLER
Voltage Reference Tolerance
Source Current
ILDGD
Sink Current
` DISABLE INPUT
ILDGD
LDO Disable
LDDIS
Note 1 – X = Phase 1, 2, 3
Note 2 – System Specification
CSS = 0.1µF
VLDFB = 0.8V, COUT = 330µF
Vout = 10V
Vout = 0.4V
Threshold
Pulldown Resistance
LX1671
Units
Min Typ Max
3.5 4.0 4.5 V
4.0 4.25 4.5
V
0.1 V
20 KΩ
0.3 V
10 %
2
30
0.2
%
ma
mA
2V
100 ΚΩ
Copyright © 2000
Rev. 1.0a, 2004-06-14
Microsemi
Integrated Products, Power Management
11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570
Page 5
5 Page 
INTEGRATED PRODUCTS
LX1671
Multiple Output LoadSHARE™ PWM
PRODUCTION DATA SHEET
THEORY OF OPERATION
GENERAL DESCRIPTION
The LX1671 is a voltage-mode pulse-width modulation
controller integrated circuit. The internal ramp generator
frequency is fixed to 300kHz. The device has external
compensation, for more flexibility of output current magnitude.
UNDER VOLTAGE LOCKOUT (UVLO)
At power up, the LX1671 monitors the supply voltage for
VCC, VCCL, and VCX (there is no requirement for sequencing
the supplies). Before all supplies reach their under-voltage lock-
out (UVLO) thresholds, the soft-start (SS) pin is held low to
prevent soft-start from beginning, the oscillator is disabled and
all MOSFETs are held off.
Hiccup is disabled during the soft-start interval, allowing start
up with maximum current. If the rate of rise of the output voltage
is too fast, the required charging current to the output capacitor
may be higher than the limit-current. In this case, the peak
MOSFET current is regulated to the limit-current by the current-
sense comparator. If the MOSFET current still reaches its limit
after the soft-start finishes, the hiccup is triggered again. When the
output has a short circuit the hiccup circuit ensures that the
average heat generation in both MOSFETs and the average current
is much less than in normal operation.
Over-current protection can also be implemented using a sense
resistor, instead of using the RDS(ON) of the upper MOSFET, for
greater set-point accuracy.
SOFT-START
Once the supplies are above the UVLO threshold, the soft-start
capacitor begins to be charged by the reference through a 20kΩ
internal resistor. The capacitor voltage at the SS pin rises as a
simple RC circuit. The SS pin is connected to the error
amplifier’s non-inverting input that controls the output voltage.
The output voltage will follow the SS pin voltage if sufficient
charging current is provided to the output capacitor.
The simple RC soft-start allows the output to rise faster at the
beginning and slower at the end of the soft-start interval. Thus,
the required charging current into the output capacitor is less at
the end of the soft-start interval. A comparator monitors the SS
pin voltage and indicates the end of soft-start when SS pin
voltage reaches 95% of VREF.
OVER-CURRENT PROTECTION (OCP) AND HICCUP
The LX1671 uses the RDS(ON) of the upper MOSFET, together
with a resistor (RSET) to set the actual current limit point. The
current sense comparator senses the MOSFET current 350nS
after the top MOSFET is switched on in order to reduce
inaccuracies due to ringing. A current source supplies a current
(ISET), whose magnitude is 50µA. The set resistor RSET is
selected to set the current limit for the application. RSET and VSX
should be connected directly at the upper MOSFET drain and
source to get an accurate measurement across the low resistance
RDS(ON).
When the sensed voltage across RDS(ON) plus the set resistor
exceeds the 300mV, VTRIP threshold, the OCP comparator outputs
a signal to reset the PWM latch and to start hiccup mode. The
soft-start capacitor (CSS) is discharged slowly (10 times slower
than when being charged up by RSS). When the voltage on the SS
pin reaches a 0.2V threshold, hiccup finishes and the circuit soft-
starts again. During hiccup both MOSFETs for that phase are
held off.
If any phase is not used connect the VSX and VCX pins to
VCC, do not leave them floating.
OSCILLATOR FREQUENCY
An internal oscillator sets the switching frequency at 300kHz.
THEORY OF OPERATION FOR A BI-PHASE, LOADSHARE
CONFIGURATION
The basic principle used in LoadSHARE, in a multiple phase
buck converter topology is that if multiple, identical, inductors
have the same identical voltage impressed across their leads, they
must then have the same identical current passing through them.
The current that we would like to balance between inductors is
mainly the DC component along with as much as possible the
transient current. All inductors in a multiphase buck converter
topology have their output side tied together at the output filter
capacitors. Therefore this side of all the inductors have the same
identical voltage.
If the input side of the inductors can be forced to have the same
equivalent DC potential on this lead, then they will have the same
DC current flowing. To achieve this requirement, phase 1 will be
the control phase that sets the output operating voltage, under
normal PWM operation. To force the current of phase 2 to be
equal to the current of phase 1, a second feedback loop is used.
Phase 2 has a low pass filter connected from the input side of each
inductor. This side of the inductors has a square wave signal that
is proportional to its duty cycle. The output of each LPF is a DC
(+ some AC) signal that is proportional to the magnitude and duty
cycle of its respective inductor signal. The second feedback loop
will use the output of the phase 1 LPF as a reference signal for an
error amplifier that will compare this reference to the output of the
phase 2 LPF. This error signal will be amplified and used to
control the PWM circuit of phase 2. Therefore, the duty cycle of
phase 2 will be set so that the equivalent voltage potential will be
forced across the phase 2 inductor as compared to the phase 1
inductor. This will force the current in the phase 2 inductor to
follow and be equal to the current in the phase 1 inductor.
There are four methods that can be used to implement the
LoadSHARE feature of the LX1671 in the Bi-Phase mode of
operation.
Copyright © 2000
Rev. 1.0a, 2004-06-14
Microsemi
Integrated Products, Power Management
11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570
Page 11
11 Page | ||
| Páginas | Total 21 Páginas | |
| PDF Descargar | [ Datasheet LX1671.PDF ] | |
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