isl62883c Intersil Corporation, isl62883c Datasheet - Page 25

• Manufacturer Part Number: isl62883c
• Description: Multiphase Pwm Regulator For Imvp-6.5? Mobile Cpus And Gpus
• Manufacturer: Intersil Corporation

Figure 21 shows the output voltage ring back problem
during load transient response. The load current i
fast step change, but the inductor current i
accurately follow. Instead, i
system fashion due to the nature of current loop. The
ESR and ESL effect of the output capacitors makes the
output voltage V
However, the controller regulates V
droop current i
of i
causing the ring back problem. This phenomenon is not
observed when the output capacitor have very low ESR
and ESL, such as all ceramic capacitors.
Figure 22 shows two optional circuits for reduction of the
ring back.
C
constant. It usually takes the parallel of two (or more)
capacitors to get the desired value. Figure 22 shows that
two capacitors C
an optional component to reduce the V
steady state, C
capacitance. At the beginning of i
capacitance is less because R
of the C
when C
ring back. This effect is more pronounced when C
much larger than C
R
ripple of the V
recommended to keep C
value usually is a few ohms. C
should be determined through tuning the load transient
response waveforms on an actual board.
R
providing a lower impedance path than R
beginning of i
effect at steady state. Through proper selection of R
and C
V
100Ω. C
FIGURE 22. OPTIONAL CIRCUITS FOR RING BACK
o
n
n
ip
L
will not ring back. The recommended value for R
is the capacitor used to match the inductor time
is bigger. However, the presence of R
and C
; therefore it pulls V
ip
n
Rntcs
n.1
values, i
ip
Rntc
is too small, and this effect will reduce the V
ip
should be determined through tuning the load
branch. As Figure 19 explains, V
form an R-C branch in parallel with R
REDUCTION
o
n
droop
n.1
change. R
Rp
signal if C
droop
n.1
o
dip quickly upon load current change.
+ C
n.2
and C
, which is a real-time representation
OPTIONAL
can resemble i
. It is also more pronounced when
n.2
o
Cn.1
n.2
ip
n.2
back to the level dictated by i
n.2
25
provides the desired C
Rn
L
and C
greater than 2200pF. R
are in parallel. Resistor R
responds in first order
n
is too small. It is
n.1
increases the impedance
, C
o
ip
o
OPTIONAL
change, the effective
do not have any
n.2
Rip
o
Cn.2
according to the
rather than i
Ri
o
and R
n
ring back. At
i
Vcn
Cip
increases the
at the
L
o
ISUM+
ISUM-
cannot
tends to dip
n
values
n
i
,
o
n.1
L
ISL62883C
has a
n
, and
ip
ip
is
n
o
is
L
is
,
transient response waveforms on an actual board. The
recommended range for C
it should be noted that the R
the i
real inductor current, i
which may adversely affect i
detection and therefore may affect OCP accuracy. User
discretion is advised.
Resistor Current-Sensing Network
Figure 23 shows the resistor current-sensing network for
a 2-phase solution. Each inductor has a series
current-sensing resistor R
connected to the R
inductor current information. The R
are connected to capacitor C
filter for noise attenuation. Equations 25 thru 27 give
V
Transfer function A
Current-sensing resistor R
significant variation over-temperature, so there is no
need for the NTC network.
The recommended values are R
C
Overcurrent Protection
Refer to Equation 1 on page 17 and Figures 17, 21 and
23; resistor R
page 21 shows the internal OCP threshold. It is
recommended to design I
resistor.
FIGURE 23. RESISTOR CURRENT-SENSING NETWORK
V
ω
Cn
A
n
Rsen
DCR
Cn
Rsen
Rsen
= 5600pF.
(s) expression
Phase1
droop
L
s ( )
s ( )
=
=
Rsen
DCR
---------------------------- -
R
-------------- -
R
-------------
waveform. Instead of being triangular as the
=
sum
N
Phase2
sen
L
Io
N
---------------------- -
1
1
i
+
×
sets the droop current I
×
------------ -
ω
1
I
C
sns
Rsen
s
DCR
o
n
s ( )
Phase3
Rsen
sen
L
×
A
droop
pads to accurately capture the
(s) always has unity gain at DC.
Rsen
droop
sen
Rsum
Rsum
Rsum
sen
ip
Ro
Ro
Ro
s ( )
may have sharp spikes,
is 100pF~2000pF. However,
droop
n
ip
. R
. R
value will not have
-C
without using the R
sum
sum
sum
ip
average value
sum
branch may distort
and R
= 1kΩ and
and C
Vcn
droop
and R
o
n
. Table 4 on
are
Cn
form a a
o
Ri
March 18, 2010
resistors
(EQ. 25)
(EQ. 26)
(EQ. 27)
ISUM+
ISUM-
FN7557.1
comp