isl6566a Intersil Corporation, isl6566a Datasheet - Page 13

• Manufacturer Part Number: isl6566a
• Description: Three-phase Buck Pwm Controller With Two Integrated Mosfet Drivers And One External Driver Signal
• Manufacturer: Intersil Corporation

Voltage Regulation
In order to regulate the output voltage to a specified level,
the ISL6566A uses the integrating compensation network
shown in Figure 6. This compensation network insures that
the steady-state error in the output voltage is limited only to
the error in the reference voltage (output of the DAC) and
offset errors in the OFS current source, remote-sense and
error amplifiers. Intersil specifies the guaranteed tolerance of
the ISL6566A to include the combined tolerances of each of
these elements.
TABLE 4. VRM10 VOLTAGE IDENTIFICATION CODES (Continued)
VID4
FIGURE 6. OUTPUT VOLTAGE AND LOAD-LINE
R
1
1
1
0
0
0
0
0
0
0
0
0
0
0
FB
EXTERNAL CIRCUIT
+
-
V
V
V
VID3
DROOP
OFS
OUT
R
0
0
0
1
1
1
1
1
1
1
1
1
1
1
+
+
-
-
C
REGULATION WITH OFFSET ADJUSTMENT
C
C
VID2
C
REF
ICOMP
0
0
0
1
1
1
1
1
1
1
1
0
0
0
COMP
VDIFF
RGND
VSEN
IREF
REF
FB
VID1
13
0
0
0
1
1
1
1
0
0
0
0
1
1
1
ISL6566A INTERNAL CIRCUIT
VID0
1k
1
0
0
1
1
0
0
1
1
0
0
1
1
0
I
OFS
VID DAC
ERROR AMPLIFIER
+
-
+
+
-
-
VID12.5
DIFFERENTIAL
REMOTE-SENSE
AMPLIFIER
0
1
0
1
0
1
0
1
0
1
0
1
0
1
V
COMP
1.4375
1.4500
1.4625
1.4750
1.4875
1.5000
1.5125
1.5250
1.5375
1.5500
1.5625
1.5750
1.5875
1.6000
VDAC
ISL6566A
The ISL6566A incorporates an internal differential remote-
sense amplifier in the feedback path. The amplifier removes
the voltage error encountered when measuring the output
voltage relative to the controller ground reference point,
resulting in a more accurate means of sensing output
voltage. Connect the microprocessor sense pins to the non-
inverting input, VSEN, and inverting input, RGND, of the
remote-sense amplifier. The droop voltage, V
feeds into the remote-sense amplifier. The remote-sense
output, V
voltage, V
the inverting input of the error amplifier through an external
resistor.
The output of the error amplifier, V
sawtooth waveform to generate the PWM signals. The PWM
signals control the timing of the Internal MOSFET drivers
and regulate the converter output so that the voltage at FB is
equal to the voltage at REF. This will regulate the output
voltage to be equal to Equation 4. The internal and external
circuitry that controls voltage regulation is illustrated in
Figure 6.
Load-Line (Droop) Regulation
Some microprocessor manufacturers require a precisely-
controlled output impedance. This dependence of output
voltage on load current is often termed “droop” or “load line”
regulation.
As shown in Figure 6, a voltage, V
total current in all active channels, I
differential remote-sense amplifier. The resulting voltage at
the output of the remote-sense amplifier is the sum of the
output voltage and the droop voltage. As Equation 4 shows,
feeding this voltage into the compensation network causes
the regulator to adjust the output voltage so that it’s equal to
the reference voltage minus the droop voltage.
The droop voltage, V
current through the output inductors. This is accomplished
by using a continuous DCR current sensing method.
Inductor windings have a characteristic distributed
resistance or DCR (Direct Current Resistance). For
simplicity, the inductor DCR is considered as a separate
lumped quantity, as shown in Figure 7. The channel current,
I
Equation 5 shows the s-domain equivalent voltage, V
across the inductor.
The inductor DCR is important because the voltage dropped
across it is proportional to the channel current. By using a
simple R-C network and a current sense amplifier, as shown
V
L
V
OUT
, flowing through the inductor, passes through the DCR.
L
s ( )
=
=
V
DIFF
I
L
OUT
REF
⋅
(
s L
, is therefore equal to the sum of the output
, and the droop voltage. V
⋅
–
V
+
OFS
DCR
DROOP
–
V
)
DROOP
, is created by sensing the
DROOP
COMP
OUT
, feeds into the
DIFF
, is compared to the
, proportional to the
is connected to
DROOP
July 27, 2005
, also
(EQ. 5)
L
FN9200.2
(EQ. 4)
,