isl6363 Intersil Corporation, isl6363 Datasheet - Page 24

• Manufacturer Part Number: isl6363
• Description: Multiphase Pwm Regulator For Vr12™ Desktop Cpus
• Manufacturer: Intersil Corporation

Figure 20 shows the output voltage ring back problem during
load transient response. The load current i
change, but the inductor current I
Instead, I
nature of current loop. The ESR and ESL effect of the output
capacitors makes the output voltage V
current change. However, the controller regulates V
the droop current I
therefore it pulls V
ring back problem. This phenomenon is not observed when the
output capacitor have very low ESR and ESL, such as all ceramic
capacitors.
Figure 21 shows two optional circuits for reduction of the ring
back.
C
usually takes the parallel of two (or more) capacitors to get the
desired value. Figure 21 shows that two capacitors C
are in parallel. Resistor R
the V
C
capacitance is less because R
C
small, and this effect will reduce the V
more pronounced when C
more pronounced when R
R
recommended to keep C
usually is a few ohms. C
determined through tuning the load transient response
waveforms on an actual board.
n
n
n.1
n
FIGURE 21. OPTIONAL CIRCUITS FOR RING BACK REDUCTION
is the capacitor used to match the inductor time constant. It
capacitance. At the beginning of i
increases the ripple of the V
branch. As Figure 18 explains, V
O
ring back. At steady state, C
FIGURE 20. OUTPUT VOLTAGE RING BACK PROBLEM
Rntcs
Rntc
L
responds in first order system fashion due to the
BACK
RING
Rp
droop
O
back to the level dictated by I
I
O
OPTIONAL
, which is a real-time representation of I
n.1
n.2
n
n.1
n
is an optional component to reduce
, C
L I
Cn.1
is bigger. However, the presence of
greater than 2200pF. R
is much larger than C
n.2
Rn
24
n
n
increases the impedance of the
signal if C
and R
L
n.1
cannot accurately follow.
O
o
+ C
tends to dip when C
O
change, the effective
V O
O
n
OPTIONAL
ring back. This effect is
dip quickly upon load
values should be
n.2
Rip
Cn.2
o
n.2
Ri
has a fast step
provides the desired
is too small. It is
Vcn
Cip
L
ISUM+
ISUM-
O
, causing the
n.2
n
according to
n.1
value
. It is also
and C
n
is too
ISL6363
n.2
L
;
R
lower impedance path than R
and C
selection of R
i
100Ω. C
transient response waveforms on an actual board. The
recommended range for C
should be noted that the R
waveform. Instead of being triangular as the real inductor
current, i
affect i
OCP accuracy. User discretion is advised.
Resistor Current-Sensing Network
Figure 22 shows the resistor current-sensing network for a
2-phase solution. Each inductor has a series current-sensing
resistor R
accurately capture the inductor current information. The R
and R
form a filter for noise attenuation. Equations 25 thru 27 give
V
Transfer function A
Current-sensing resistor R
variation over-temperature, so there is no need for the NTC
network.
The recommended values are R
V
ω
A
L
Cn
ip
Cn
, and V
Rsen
Rsen
Rsen
DCR
(s) expression
and C
s ( )
Phase1
L
ip
o
s ( )
droop
FIGURE 22. RESISTOR CURRENT-SENSING NETWORK
=
resistors are connected to capacitor C
=
do not have any effect at steady state. Through proper
O
ip
droop
ip
---------------------------
R
------------- -
sen
R
------------
=
will not ring back. The recommended value for R
should be determined through tuning the load
Rsen
sum
DCR
sen
N
N
form an R-C branch in parallel with R
----------------------
1
. R
average value detection and therefore may affect
Phase2
L
Io
ip
1
+
may have sharp spikes, which may adversely
×
×
sum
and C
1
------------
ω
I
C
o
sns
s
n
s ( )
Rsen
Rsen
DCR
and R
Phase3
ip
×
L
A
values, i
(s) always has unity gain at DC.
Rsen
o
sen
ip
ip
are connected to the R
is 100pF~2000pF. However, it
-C
s ( )
value will not have significant
i
Rsum
Rsum
Rsum
at the beginning of i
ip
Ro
Ro
Ro
sum
droop
branch may distort the i
= 1kΩ and C
can resemble i
Vcn
n
. R
n
i
September 29, 2011
, providing a
sum
= 5600pF.
sen
Cn
o
o
Ri
change. R
rather than
and C
pads to
droop
ISUM+
ISUM-
FN6898.0
(EQ. 25)
(EQ. 26)
(EQ. 27)
sum
ip
n
is
ip