isl6566a Intersil Corporation, isl6566a Datasheet - Page 21

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

dissipation in the controller itself, P
estimated as:
Current Balancing Component Selection
The ISL6566A senses the channel load current by sampling
the voltage across the lower MOSFET r
Figure 17. The ISEN pins are denoted ISEN1, ISEN2, and
ISEN3. The resistors connected between these pins and the
respective phase nodes determine the gains in the channel-
current balance loop.
Select values for these resistors based on the room
temperature r
operating current, I
Equation 24.
In certain circumstances, it may be necessary to adjust the
value of one or more ISEN resistors. When the components of
one or more channels are inhibited from effectively dissipating
their heat so that the affected channels run hotter than
desired, choose new, smaller values of R
phases (see the section entitled Channel-Current Balance).
Choose R
R
P
P
P
R
P
FIGURE 17. ISL6566A INTERNAL AND EXTERNAL CURRENT-
ISEN
DR
DR_UP
DR_LOW
EXT1
BOOT
ISL6566A
=
=
P
=
=
DR_UP
=
---------------------- -
50 10
r
R
ISEN,2
DS ON
=
P
---------------------



G1
Qg_Q1
--------------------------------------
R
×



(
SENSING CIRCUITRY
DS(ON)
HI1
--------------------------------------
R
3
+
HI2
–
+
R
-------------
R
N
6
)
in proportion to the desired decrease in
+
P
GI1
ISEN(n)
HI1
Q1
R
I
------- -
R
+
DR_LOW
FL
FL
N
HI2
CHANNEL N
LOWER MOSFET
EXT1
R
of the lower MOSFETs; the full-load
; and the number of phases, N using
EXT2
R
ISEN
+
+
--------------------------------------- -
R
+
21
LO1
--------------------------------------- -
R
P
R
V
LO2
IN
BOOT
EXT2
R
+
+
CHANNEL N
UPPER MOSFET
-
LO1
R
I L r DS ON
+
DR
R
LO2
EXT1
R
+
=
, can be roughly
EXT2
I
(
L
R
I
DS(ON)
Q
(
ISEN
G2



•
•



VCC
+
)
P
---------------------
•
R
-------------
for the affected
Qg_Q1
N
P
---------------------
GI2
, as shown in
Q2
Qg_Q2
3
)
2
(EQ. 23)
(EQ. 24)
ISL6566A
temperature rise in order to cause proportionally less current
to flow in the hotter phase.
In Equation 25, make sure that ∆T
rise above the ambient temperature, and ∆T
temperature rise above the ambient temperature. While a
single adjustment according to Equation 25 is usually
sufficient, it may occasionally be necessary to adjust R
two or more times to achieve optimal thermal balance
between all channels.
Load Line Regulation Component Selection (DCR
Current Sensing)
For accurate load line regulation, the ISL6566A senses the
total output current by detecting the voltage across the
output inductor DCR of each channel (As described in the
Load Line Regulation section). As Figure 18 illustrates, an
R-C network is required to accurately sense the inductor
DCR voltage and convert this information into a “droop”
voltage, which is proportional to the total output current.
Choosing the components for this current sense network is a
two step process. First, R
chosen so that the time constant of this R
network matches the time constant of the inductor L/DCR.
Then the resistor R
sense network gain, obtaining the desired full load droop
voltage. Follow the steps below to choose the component
values for this R-C network.
R
1. Choose an arbitrary value for C
2. Plug the inductor L and DCR component values, and the
3. Use the new value for R
ISEN 2 ,
value is 0.01µF.
values for C
calculate the value for R
26, as well as the desired full load current, I
droop voltage, V
27 to calculate the value for R
R
R
COMP
S
=
=
------------------------ - R
V
R
DROOP
=
ISEN
I
FL
---------------------------------------
DCR C
COMP
∆T
----------
∆T
⋅
S
⋅
2
1
DROOP
L
must be chosen to set the current
COMP
COMP
chosen in steps 1, into Equation 26 to
COMP
, and inductor DCR in Equation
⋅
COMP
COMP
DCR
and C
2
S
COMP
.
is the desired temperature
obtained from Equation
.
COMP
. The recommended
COMP
1
is the measured
must be
FL
-C
, full load
COMP
July 27, 2005
(EQ. 25)
(EQ. 26)
(EQ. 27)
ISEN
FN9200.2