ISL62881CHRTZ-T Intersil, ISL62881CHRTZ-T Datasheet - Page 20

• Manufacturer Part Number: ISL62881CHRTZ-T
• Description: IC REG PWM SGL PHASE 28TQFN
• Manufacturer: Intersil

Specifications of ISL62881CHRTZ-T

• Applications: Controller, Intel IMVP-6.5™
• Voltage - Input: 4.5 ~ 25 V
• Number Of Outputs: 1
• Voltage - Output: 0.0125 ~ 1.5 V
• Operating Temperature: -10°C ~ 100°C
• Mounting Type: Surface Mount
• Package / Case: 28-VQFN
• For Use With: ISL62881CCPUEVAL2Z - EVAL BOARD ISL62881CCPU 28QFN
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

Figure 17 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 capacitors have very low ESR
and ESL, such as all ceramic capacitors.
Figure 18 shows two optional circuits for reduction of the
ring back. R
with R
the beginning of i
any effect at steady state. Through proper selection of
R
i
for R
tuning the load transient response waveforms on an
actual board. The recommended range for C
100pF~2000pF. However, it should be noted that the
R
Instead of being triangular as the real inductor current,
i
affect i
may affect OCP accuracy. User discretion is advised.
FIGURE 18. OPTIONAL CIRCUITS FOR RING BACK
L
droop
FIGURE 17. OUTPUT VOLTAGE RING BACK PROBLEM
ip
ip
, and V
L
and C
-C
; therefore it pulls V
ip
Rntcs
ip
i
may have sharp spikes, which may adversely
Rntc
, providing a lower impedance path than R
droop
is 100Ω. C
branch may distort the i
o
ip
will not ring back. The recommended value
BACK
ip
RING
values, i
REDUCTION
average value detection and therefore
Rp
and C
droop
o
i
O
ip
o
dip quickly upon load current change.
OPTIONAL
, which is a real-time representation
change. R
should be determined through
ip
droop
i
L
Cn.1
form an R-C branch in parallel
o
Rn
back to the level dictated by i
20
can resemble i
L
responds in first order
ip
V
and C
O
OPTIONAL
droop
Rip Cip
o
Cn.2
+
according to the
-
Ri
ip
waveform.
Vcn
ISL62881C, ISL62881D
ISL62881C, ISL62881D
do not have
ISUM+
o
ISUM-
L
rather than
cannot
ip
is
o
has a
i
at
L
,
C
constant. It usually takes the parallel of two (or more)
capacitors to get the desired value. Figure 18 shows
that two capacitors C
Resistor R
ring back. At steady state, C
desired C
the effective capacitance is less because R
the impedance of the C
explains, V
effect will reduce the V
pronounced when C
also more pronounced when R
presence of R
C
greater than 2200pF. R
C
through tuning the load transient response waveforms
on an actual board.
Resistor Current-Sensing Network
Figure 19 shows the resistor current-sensing network.
The inductor has a series current-sensing resistor R
R
capture the inductor current information. The R
the sensed information to capacitor C
form a a filter for noise attenuation. Equations 13
through 15 gives V
V
A
ω
FIGURE 19. RESISTOR CURRENT-SENSING NETWORK
sum
n
n.2
n.1
Cn
Rsen
Rsen
is the capacitor used to match the inductor time
s ( )
, C
is too small. It is recommended to keep C
and is connected to the R
s ( )
=
=
n.2
RSEN
DCR
---------------------------- -
R
R
=
n
n
sum
sen
PHASE
Io
o
and R
L
---------------------- -
1
capacitance. At the beginning of i
is an optional component to reduce the V
+
tends to dip when C
1
×
n
×
1
------------ -
ω
I
sns
C
o
s
increases the ripple of the V
s ( )
n
n
Cn
values should be determined
×
RSUM
n.1
A
(s) expressions:
n.1
Rsen
o
n
n.1
is much larger than C
ring back. This effect is more
and C
value usually is a few ohms.
Vcn
s ( )
branch. As Figure 15
n.1
n
sen
n.2
is bigger. However, the
+ C
n
Cn
is too small, and this
pad to accurately
are in parallel.
Ri
n.2
n
. R
provides the
sum
ISUM+
ISUM-
n
n
increases
and C
o
n.2
sum
March 8, 2010
signal if
change,
n.2
. It is
(EQ. 13)
(EQ. 14)
(EQ. 15)
FN7596.0
feeds
sen
n
.
o