ISL6327IRZ-T Intersil, ISL6327IRZ-T Datasheet - Page 24

• Manufacturer Part Number: ISL6327IRZ-T
• Description: IC CTRLR PWM 6PHASE BUCK 48-QFN
• Manufacturer: Intersil

Specifications of ISL6327IRZ-T

• Pwm Type: Voltage Mode
• Number Of Outputs: 1
• Frequency - Max: 275kHz
• Duty Cycle: 25%
• 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: -40°C ~ 85°C
• Package / Case: 48-VQFN
• Frequency-max: 275kHz
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

ramps up to assume the full inductor current. In Equation 26,
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 draw 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 29 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 26, 27, 28 and 29. 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 Resistor
The resistors connected to the Isen+ pins determine the
gains in the load-line regulation loop and the channel-current
balance loop as well as setting the overcurrent trip point.
Select values for these resistors by the Equation 30.
where R
pin, N is the active channel number, R
the current sense element, either the DCR of the inductor or
R
desired overcurrent trip point. Typically, I
to be 1.3 times the maximum load current of the specific
application.
With integrated temperature compensation, the sensed
current signal is independent on the operational temperature
of the power stage, i.e. the temperature effect on the current
sense element R
temperature compensation function. R
should be the resistance of the current sense element at the
room temperature.
P
P
P
P
R
SENSE
UP 1 ,
UP 2 ,
UP 3 ,
UP 4 ,
ISEN
≈
≈
≈
=
=
r
V
V
DS ON
ISEN
V
depending on the sensing method, and I
IN
IN
---------------------- -
85 10
IN
(
⎛
⎝
⎛
⎜
⎝
R
×
I
----- -
Q
I
----- -
N
N
M
M
X
is the sense resistor connected to the ISEN+
rr
)
+
–
–
f
S
⎛
⎜
⎝
6
I
-------- -
I
-------- -
X
UP,4
PP
PP
I
----- -
N
2
2
M
I
------------- -
OCP
is cancelled by the integrated
rr
⎞
⎟
⎠
⎞ t
⎠
⎞ t
⎟
⎠
N
. Since the inductor current has fully
2
⎛
⎜
⎝
⎛
⎜
⎝
.
d
----
----
2
2
2
1
+
⎞
⎟
⎠
⎞
⎟
⎠
I
--------- - d
f
f
UP,3
PP
12
S
S
2
UP,2
24
2
and is approximately
. In Equation 27, the
.
X
X
is the resistance of
OCP
rr
in Equation 30
UP,1
1
, it is conducted
and the
can be chosen
.
OCP
(EQ. 29)
(EQ. 26)
(EQ. 27)
(EQ. 28)
(EQ. 30)
is the
ISL6327
When the integrated temperature compensation function is
disabled by pulling the TCOMP pin to GND, the sensed
current will be dependent on the operational temperature of
the power stage, since the DC resistance of the current
sense element may be changed according to the operational
temperature. R
resistance of the current sense element at all the operational
temperature.
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 RISEN for the
affected phases (see the section titled “Channel-Current
Balance” on page 12). Choose R
desired decrease in temperature rise in order to cause
proportionally less current to flow in the hotter phase.
In Equation 31, make sure that ΔT
rise above the ambient temperature, and ΔT
temperature rise above the ambient temperature. While a
single adjustment according to Equation 31 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 Resistor
The load-line regulation resistor is labelled R
Its value depends on the desired loadline requirement of the
application.
The desired loadline can be calculated using Equation 32:
where I
and VR
load condition.
Based on the desired loadline R
resistor can be calculated using Equation 33:
where N is the active channel number, R
resistor connected to the ISEN+ pin, and R
resistance of the current sense element, either the DCR of
the inductor or R
If one or more of the current sense resistors are adjusted for
thermal balance, as in Equation 31, the load-line regulation
resistor should be selected based on the average value of
the current sensing resistors, as given in Equation 34:
R
R
R
ISEN 2 ,
LL
FB
=
=
V
------------------------ -
FL
N R
--------------------------------- -
DROOP
DROOP
=
I
is the full load current of the specific application,
FL
ISEN
R
R
ISEN
X
X
R
is the desired voltage droop under the full
SENSE
LL
in Equation 30 should be the maximum DC
ΔT
----------
ΔT
2
1
depending on the sensing method.
LL
ISEN,2
2
, the loadline regulation
is the desired temperature
in proportion to the
ISEN
1
X
is the measured
FB
is the
is the sense
in Figure 5.
May 5, 2008
(EQ. 33)
(EQ. 31)
(EQ. 32)
ISEN
FN9276.4