isl62883c Intersil Corporation, isl62883c Datasheet - Page 27

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

A capacitor C
the IMON pin voltage. The R
the user’s choice. It is recommended to have a time
constant long enough such that switching frequency
ripples are removed.
Compensator
Figure 18 shows the desired load transient response
waveforms. Figure 24 shows the equivalent circuit of a
voltage regulator (VR) with the droop function. A VR is
equivalent to a voltage source (= VID) and output
impedance Z
slope LL, i.e. constant output impedance, in the entire
frequency range, V
has a square change.
Intersil provides a Microsoft Excel-based spreadsheet to
help design the compensator and the current sensing
network, so the VR achieves constant output impedance
as a stable system. Figure 27 shows a screenshot of the
spreadsheet.
A VR with active droop function is a dual-loop system
consisting of a voltage loop and a droop loop which is a
current loop. However, neither loop alone is sufficient to
describe the entire system. The spreadsheet shows two
loop gain transfer functions, T1(s) and T2(s), that
describe the entire system. Figure 25 conceptually
shows T1(s) measurement set-up and Figure 26
conceptually shows T2(s) measurement set-up. The VR
senses the inductor current, multiplies it by a gain of
the load line slope, then adds it on top of the sensed
output voltage and feeds it to the compensator. T(1) is
measured after the summing node, and T2(s) is
measured in the voltage loop before the summing node.
The spreadsheet gives both T1(s) and T2(s) plots.
However, only T2(s) can be actually measured on an
ISL62883C regulator.
FIGURE 24. VOLTAGE REGULATOR EQUIVALENT
VID
out
CIRCUIT
imon
(s). If Z
Z
can be paralleled with R
out
o
(s) = LL
will have square response when I
out
VR
27
(s) is equal to the load line
imon
i
o
C
imon
LOAD
time constant is
imon
V
o
to filter
ISL62883C
o
T1(s) is the total loop gain of the voltage loop and the
droop loop. It always has a higher crossover frequency
than T2(s) and has more meaning of system stability.
T2(s) is the voltage loop gain with closed droop loop. It
has more meaning of output voltage response.
Design the compensator to get stable T1(s) and T2(s)
with sufficient phase margin, and output impedance
equal or smaller than the load line slope.
FIGURE 25. LOOP GAIN T1(s) MEASUREMENT SET-UP
FIGURE 26. LOOP GAIN T2(s) MEASUREMENT SET-UP
V IN
V in
LOOP GAIN =
LOOP GAIN=
DRIVER
DRIVER
Q1
GATE
Q1
GATE
MOD.
MOD.
Q2
CHANNEL A
CHANNEL B
CHANNEL B
CHANNEL A
Q2
COMP
ANALYZER
NETWORK
CHANNEL A
COMP
LOAD LINE SLOPE
ANALYZER
CHANNEL A
NETWORK
EA
L
LOAD LINE SLOPE
C OUT
EA
L
VID
C out
VID
EXCITATION OUTPUT
EXCITATION OUTPUT
V O
20
V o
I
O
20
Ω
o i
Ω
ISOLATION
TRANSFORMER
ISOLATION
TRANSFORMER
CHANNEL B
March 18, 2010
CHANNEL B
FN7557.1