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PDF LX1672 Data sheet ( Hoja de datos )
| Número de pieza | LX1672 | |
| Descripción | Multiple Output LoadSHARE PWM | |
| Fabricantes | Microsemi Corporation | |
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LX1672
TM ® Multiple Output LoadSHARE™ PWM
PRELIMINARY DATA SHEET
DESCRIPTION
The LX1672 is a highly integrated This patented approach also gives
power supply controller IC featuring system designers maximum flexibility with
www.tDwaotaShPeWet4MU.nestwitching regulator stages respect to MOSFET supply. Each phase
with an additional onboard linear can utilize different supply voltages, for
regulator driver.
efficient use of available supplies, while
The two constant frequency voltage- programming the ratio of current pulled
mode PWM phases can be easily from each using one of three methods (see
configured as a single Bi-Phase high application section).
current output, two independently The LX1672 incorporates fully
regulated outputs, or as a DDR memory programmable soft-start sequencing
I/O supply with a tracking DDR capabilities. Each output can be
termination voltage supply. Power loss configured to come up in any order
and noise, due to the ESR of the input necessary as required by the application.
capacitors, are minimized by operating The LX1672 features an additional
each PWM output 180° out of phase. Linear Regulator Driver output, which
This architecture also minimizes when coupled with an inexpensive
capacitor
requirements
while MOSFET is capable of supplying up to 5A
maximizing regulator response.
for I/O, memory, and other supplies
In bi-phase operation, the high surrounding today’s micro-processor
current output utilizes a patented current designs.
sharing architecture, called Forced Each regulator voltage output is
Current Sharing†, to allow accurate programmed via a simple voltage-divider
current sharing without the use of network. The LX1672, utilizing MOSFET
expensive current sense resistors.
RDS(ON) impedance, monitors maximum
current limit conditions, in each PWM
phase without the use of expensive current
sense resistors.
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 Three Independently
Regulated Outputs
DDR Termination Compliant
Bi-phase Current Sharing
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, 500KHz and 600KHz
High Frequency Operation
Minimizes External Component
Requirements
Independent Phase Programmable
Soft-Start and Power Sequencing
Adjustable Linear Regulator Driver
Output
No current-sense resistors
APPLICATIONS/BENEFITS
Multi-Output Power Supplies
Video Card Power Supplies
DDR, VDDQ and Termination
Supply
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
3.3V
LX1672
Graphics
Controller
Memory Bus
I/O
DDR Mem ory
TA (°C)
0 to 70
0 to 70
0 to 70
Switching
Frequency (kHz)
300
500
600
PACKAGE ORDER INFO
Plastic TSSOP
PW 28-Pin
RoHS Compliant / Pb-free Transition DC: 0518
LX1672-03CPW
LX1672-05CPW
Plastic MLPQ
LQ 38-Pin
RoHS Compliant / Pb-free Transition DC: 0512
LX1672-03CLQ
LX1672-06CLQ
NOTE: Available in Tape & Reel. Append the letters “TR” to the part number (i.e. LX1672-06CLQ-TR)
Copyright © 2000
Rev. 0.3m, 2005-04-12
Microsemi
Linfinity Microelectronics Division
11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570
Page 1
1 page  
LX1672
TM ® Multiple Output LoadSHARE™ PWM
PRELIMINARY DATA SHEET
ELECTRICAL CHARACTERISTICS
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
IHDRV
Sink Current
` DISABLE INPUT
ILDRV
CSS = 0.1µF
VLDFB = 0.8V, COUT = 330µF
Vout = 10V
Vout = 0.4V
PWM Disable
DISX
Pulldown Resistance
LDO Disable
LDDIS Pulldown Resistance
Note 1 –X = Phase 1,2
Note 2 – System Specification
LX1672
Units
Min Typ Max
3.5 4.0 4.5 V
4.0 4.25 4.5
V
0.1 V
20 KΩ
0.15 V
10 %
2
30
0.2
%
mA
mA
1.0 V
80 ΚΩ
2.5 V
100 KΩ
Copyright © 2000
Rev. 0.3m, 2005-04-12
Microsemi
Linfinity Microelectronics Division
11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570
Page 5
5 Page 
LX1672
TM ® Multiple Output LoadSHARE™ PWM
PRELIMINARY DATA SHEET
THEORY OF OPERATION (CONTINUED)
BI-PHASE, LOADSHARE ( ESR METHOD)
The first method is to change the ratio of the inductors
equivalent series resistance, (ESR). As can be seen in the previous
example, if the offset error is zero and the ESR of the two
inductors are identical, then the two inductor currents will be
identical. To change the ratio of current between the two
inductors, the value of the inductor’s ESR can be changed to allow
more current to flow through one inductor than the other. The
inductor with the lower ESR value will have the larger current.
The inductor currents are directly proportional to the ratio of the
inductor’s ESR value.
The following circuit description shows how to select the
inductor ESR for each phase where a different amount of power is
taken from two different input power supplies. A typical setup will
have a +5V power supply connected to the phase 1 half bridge
driver and a +3.3V power supply connected to the phase 2 half
bridge driver. The combined power output for this core voltage is
18W (+1.5V @ 12A). For this example the +5V power supply will
supply 7W and the +3.3V power supply will supply the other 11W.
7W @ 1.5V is a 4.67A current through the phase 1 inductor. 11W
@ 1.5V is a 7.33A current through the phase 2 inductor. The
ratio of inductor ESR is inversely proportional to the power level
split.
ESR1
ESR2
=
I2
I1
The higher current inductor will have the lower ESR value. If
the ESR of the phase 1 inductor is selected as 10mΩ, then the ESR
value of the phase 2 inductor is calculated as:
⎜⎛ 4.67 A ⎟⎞ × 10 mΩ = 6.4 mΩ
⎝ 7.33A ⎠
Depending on the required accuracy of this power sharing;
inductors can be chosen from standard vendor tables with an ESR
ratio close to the required values. Inductors can also be designed
for a given application so that there is the least amount of
compromise in the inductor’s performance.
+5V @ 7W
L1
4.67A
1.5V +
10mΩ
VOUT
46.7mV
6.4mΩ
1.5V @ 12A
+3.3V @ 11W L2
7.33A
18W
BI-PHASE, LOADSHARE ( FEEDBACK DIVIDER METHOD)
Sometimes it is desirable to use the same inductor in both phases
while having a much larger current in one phase versus the other. A
simple resistor divider can be used on the input side of the Low Pass
Filter that is taken off of the switching side of the inductors. If the
Phase 2 current is to be larger than the current in Phase 1; the resistor
divider is placed in the feedback path before the Low Pass Filter that
is connected to the Phase 2 inductor. If the Phase 2 current needs to
be less than the current in Phase 1; the resistor divider is then placed
in the feedback path before the Low Pass Filter that is connected to
the Phase 1 inductor.
As in Figure 7, the millivolts of DC offset created by the resistor
divider network in the feedback path, appears as a voltage generator
between the ESR of the two inductors.
A divider in the feedback path from Phase 2 will cause the
voltage generator to be positive at Phase 2. With a divider in the
feedback path of Phase 1 the voltage generator becomes positive at
Phase 1. The Phase with the positive side of the voltage generator
will have the larger current. Systems that operate continuously
above a 30% power level can use this method, a down side is that
that the current difference between the two inductors still flows
during a no load condition.
This produces a low efficiency condition during a no load or light
load state, this method should not be used if a wide range of output
power is required.
The following description and Figure 8 show how to determine
the value of the resistor divider network required to generate the
offset voltage necessary to produce the different current ratio in the
two output inductors. The power sharing ratio is the same as that of
Figure 7. The Offset Voltage Generator is symbolic for the DC
voltage offset between Phase 1 & 2. This voltage is generated by
small changes in the duty cycle of Phase 2. The output of the LPF is
a DC voltage proportional to the duty cycle on its input. A small
amount of attenuation by a resistor divider before the LPF of Phase 2
will cause the duty cycle of Phase 2 to increase to produce the added
offset at V2. The high DC gain of the error amplifier will force
LPF2 to always be equal to LPF1. The following calculations
determine the value of the resistor divider necessary to satisfy this
example.
Figure 7 – Ratio LoadSHARE Using Inductor ESR
Copyright © 2000
Rev. 0.3m, 2005-04-12
Microsemi
Linfinity Microelectronics Division
11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570
Page 11
11 Page | ||
| Páginas | Total 20 Páginas | |
| PDF Descargar | [ Datasheet LX1672.PDF ] | |
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