lx1676 Microsemi Corporation, lx1676 Datasheet - Page 11

• Manufacturer Part Number: lx1676
• Description: Mobile Amd Athlontm Vrm Controller
• Manufacturer: Microsemi Corporation

Copyright © 2000
Revision: 1.0, 4/12/2005
T
L
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 has the same
identical voltage.
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
magnitude and duty cycle of its respective inductor signal.
HEORY OF
OAD
The basic principle used in LoadSHARE
If the input side of the inductors can be forced to have
SHARE
TM
(+ some AC) signal that is proportional to the
DC Bias
LP1
LP2
O
PERATION FOR A
TM
C
ONFIGURATION
11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: [phone]
Low Pass Filter
Low Pass Filter
Phase 2
Phase 1
Differential Feedbach From Vout
+
-
Differential
T H E O R Y O F O P E R A T I O N ( C O N T I N U E D )
Amp
B
I
-P
HASE
DC Bias
EA -
Figure 5 – LoadSHARE Control Loop
,
TM
Integrated Products Division
in a multiple
-
Phase 1 Diff
Integrating
Amp
Phase 2
DC Bias
DACOUT
Amp
®
Microsemi
EO2
Phase 1 Error
-
+
-
Amp
gm
Ramp .75 V to 3 V
phase 1 LPF as a reference signal for an error amplifier
that will compare this reference to the output of the phase 2
LPF.
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 equal the
phase 1 inductor current.
imbalance the phases so that one phase will supply more
current than the other under unique situations. The LX1676
will normally be used with the same supply voltages on
phase 1 and 2 PWM inputs and will have equal currents in
both phases.
Mobile AMD Athlon™ VRM Controller
Both PWMs
The second feedback loop will use the output of the
With the LoadSHARE
180°
0°
This error signal will be amplified and used to
Comparator
+
_
_
+
Comparator
Phase 1
P
Phase 2
RODUCTION
HO1
LO1
HO2
LO2
TM
D
ATA
topology it is possible to
S
HEET
Vout
LX1676
Page 11