ISL62883HRTZ-T Datasheet, PDF (23/37 Pages) Intersil Corporation – Multiphase PWM Regulator for IMVP-6.5™ Mobile CPUs

ISL62883, ISL62883B
Zout(s)=LL
io
VID
VR
Load Vo
FIGURE 21. VOLTAGE REGULATOR EQUIVALENT CIRCUIT
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. Please
contact Intersil Application support at www.intersil.com/design/.
Figure 24 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 22
conceptually shows T1(s) measurement set-up and Figure 23
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 ISL62883 regulator.
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.
Q1
Vin
GATE Q2
DRIVER
L
Vo
Cout
io
LOAD LINE SLOPE
20Ω
Mod.
EA
Comp
VID
LOOP GAIN = ^{CHANNEL B}
CHANNEL A
ISOLATION
TRANSFORMER
CHANNEL A
NETWORK
ANALYZER
EXCITATION
OUTPUT
CHANNEL B
FIGURE 22. LOOP GAIN T1(s) MEASUREMENT SET-UP
Q1
Vin
GATE Q2
DRIVER
L
Vo
Cout
io
LOAD LINE SLOPE
Mod.
EA Ω
Comp
VID
LOOP GAIN = ^{CHANNEL B}
CHANNEL A
CHANNEL A
NETWORK
ANALYZER
20
ISOLATION
TRANSFORMER
EXCITATION
OUTPUT
CHANNEL B
FIGURE 23. LOOP GAIN T2(s) MEASUREMENT SET-UP
23
FN6891.4
June 21, 2011