ISL6308ACRZ-T Intersil, ISL6308ACRZ-T Datasheet - Page 13

• Manufacturer Part Number: ISL6308ACRZ-T
• Description: IC CTRLR PWM BUCK 3PHASE 40-QFN
• Manufacturer: Intersil

Specifications of ISL6308ACRZ-T

• Pwm Type: Voltage Mode
• Number Of Outputs: 1
• Frequency - Max: 275kHz
• Duty Cycle: 66.6%
• Voltage - Supply: 4.75 V ~ 5.25 V
• Buck: Yes
• Boost: No
• Flyback: No
• Inverting: No
• Doubler: No
• Divider: No
• Cuk: No
• Isolated: No
• Operating Temperature: 0°C ~ 70°C
• Package / Case: 40-VFQFN, 40-VFQFPN
• Frequency-max: 275kHz
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

Load-Line (Droop) Regulation
In some high current applications, a requirement on a
precisely controlled output impedance is imposed. This
dependence of output voltage on load current is often
termed “droop” or “load line” regulation.
The Droop is an optional feature in the ISL6308A. It can be
enabled by connecting ICOMP pin to DROOP pin, as shown
in Figure 6. To disable it, connect the DROOP pin to IREF pin.
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,
R
FIGURE 6. OUTPUT VOLTAGE AND LOAD-LINE
1
V
C
DROOP
EXTERNAL CIRCUIT
SUM
+
-
V
V
OUT
OFS
R
+
+
-
-
2
REGULATION WITH OFFSET ADJUSTMENT
R
C
S1
1
C
DROOP
REF
ICOMP
COMP
VDIFF
VSEN
RGND
ISUM
IREF
REF
R
DROOP
DAC
FB
P1
, is created by sensing the
13
ISL6308A INTERNAL CIRCUIT
DROOP
I
OUT
OFS
VID DAC
+
-
, feeds into the
ERROR AMPLIFIER
+
+
, proportional to the
ISENSE
-
-
AMP
REMOTE-SENSE
DIFFERENTIAL
AMPLIFIER
+
-
V
COMP
ISL6308A
I
Equation 6 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
in Figure 7, the voltage drop across all of the inductors DCRs
can be extracted. The output of the current sense amplifier,
V
currents I
If the R-C network components are selected such that the
R-C time constant matches the inductor L/DCR time
constant, then V
drops across the individual DCRs, multiplied by a gain. As
Equation 8 shows, V
total output current, I
V DROOP s ( )
V
L
V
DROOP
DROOP
, flowing through the inductor, passes through the DCR.
L
s ( )
V
ISL6308A
DROOP
=
+
-
, can be shown to be proportional to the channel
I
FIGURE 7. DCR SENSING CONFIGURATION
L1
L
=
PHASE1
PHASE2
DROOP
⋅
=
, I
R
-------------------- - I
(
IREF
s L
ICOMP
------------------------------------------------------------------------- -
(
COMP
L2
ISUM
s R COMP C COMP
R
⋅
⋅
S
, and I
DROOP
+
DCR
⋅
⎛
⎝
DROOP
-------------
DCR
OUT
s L
OUT
L3
⋅
)
⋅
C
, shown in Equation 7.
is equal to the sum of the voltage
.
+
SUM
⋅
(OPTIONAL)
C
1
DCR
COMP
⎞
⎠
is therefore proportional to the
R
S
+
1
R
R
)
S
COMP
⋅
R COMP
-----------------------
I
I
L2
L1
INDUCTOR
INDUCTOR
R S
L1
L2
V
L
(s)
⋅
(
DCR
DCR
I L1
-
September 9, 2008
+
I L2
(EQ. 6)
+
L
FN6669.0
(EQ. 8)
C
(EQ. 7)
I
,
I L3
OUT
V
OUT
OUT
) DCR
⋅