ISL6565 Intersil Corporation, ISL6565 Datasheet - Page 20

• Manufacturer Part Number: ISL6565
• Description: Multi-Phase PWM Controller with Precision rDS(ON) or DCR Current Sensing for VR10.X Application
• Manufacturer: Intersil Corporation

the required time for this commutation is t
approximated associated power loss is P
At turn on, the upper MOSFET begins to conduct and this
transition occurs over a time t
approximate power loss is P
A third component involves the lower MOSFET’s reverse-
recovery charge, Q
commutated to the upper MOSFET before the lower-
MOSFET’s body diode can recover all of Q
through the upper MOSFET across VIN. The power
dissipated as a result is P
Finally, the resistive part of the upper MOSFET’s is given in
Equation 25 as P
The total power dissipated by the upper MOSFET at full load
can now be approximated as the summation of the results
from Equations 22, 23, 24 and 25. Since the power
equations depend on MOSFET parameters, choosing the
correct MOSFETs can be an iterative process involving
repetitive solutions to the loss equations for different
MOSFETs and different switching frequencies.
Current Sensing Component Selection
The ISL6565A supports MOSFET r
while the ISL6565B uses inductor DCR current sensing. The
procedures for choosing the components for each method of
current sensing are very different an are described in the
next two sections.
MOSFET r
The ISL6565A senses the channel load current by sampling
the voltage across the lower MOSFET r
Figure 15. 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 load-line
regulation loop and the channel-current balance loop as well
as setting the over-current trip point.
P
P
P
P
P
UP 1 ,
UP 2 ,
UP 2 ,
UP 3 ,
UP 4 ,
≈
≈
≈
≈
=
V
r
V
V
DS ON
V
IN
IN
IN
IN
DS(ON)
(








I
----- -
Q
I
I
----- -
----- -
N
N
N
M
M
M
rr
)
+
–
–
f
S



I
-------- -
I
I
-------- -
-------- -
UP,4
PP
PP
PP
I
----- -
2
2
2
N
M
SENSING (ISL6565A ONLY)
rr



 t

 t
 t




. Since the inductor current has fully
2









.
d
----
----
----
2
2
2
2
2
1
+









I
--------- -
f
f
f
UP,3
PP
12
S
S
S
2
UP,2
20
2
.
. In Equation 23, the
.
DS(ON)
DS(ON)
UP,1
1
rr
current sensing,
and the
, it is conducted
.
, as shown in
ISL6565A, ISL6565B
(EQ. 22)
(EQ. 23)
(EQ. 24)
(EQ. 25)
Select values for these resistors based on the room
temperature r
operating current, I
Equation 26.
In certain circumstances, it may be necessary to adjust the
value of one or more ISEN resistor. When the components of
one or more channels are inhibited from effectively dissipating
their heat so that the affected channels run hotter than
desired, chose new, smaller values of R
phases (see the section entitled Voltage Regulation). Choose
R
rise in order to cause proportionally less current to flow in the
hotter phase.
In Equation 27, make sure that ∆T
rise above the ambient temperature, and ∆T
temperature rise above the ambient temperature. While a
single adjustment according to Equation 27 is usually
sufficient, it may occasionally be necessary to adjust R
two or more times to achieve optimal thermal balance
between all channels.
INDUCTOR DCR SENSING (ISL6565B ONLY)
The ISL6565B senses the channel load current by sampling
the voltage across the output inductor DCR, as described in
the Current Sensing section. As Figure 16 illustrates, an R-C
network across the inductor is required to sense the channel
current accurately.
R
R
FIGURE 15. ISL6565A INTERNAL AND EXTERNAL CURRENT-
ISEN,2
ISEN
ISEN 2 ,
ISL6565A
=
in proportion to the desired decrease in temperature
=
---------------------- -
70 10
r
DS ON
R
×
ISEN
(
SENSING CIRCUITRY
DS(ON)
–
6
)
ISEN(n)
∆T
----------
∆T
I
------- -
FL
FL
N
CHANNEL N
LOWER MOSFET
2
1
; and the number of phases, N using
of the lower MOSFETs; the full-load
R
ISEN
V
IN
+
2
CHANNEL N
UPPER MOSFET
-
I
L
is the desired temperature
r
DS ON
I
L
ISEN
(
1
)
is the measured
for the affected
(EQ. 26)
(EQ. 27)
ISEN