ISL6580CR Intersil, ISL6580CR Datasheet - Page 23

• Manufacturer Part Number: ISL6580CR
• Description: IC DRIVER HIGH SIDE FET 56-QFN
• Manufacturer: Intersil
• Type: High Side/Low Side Driverr

Specifications of ISL6580CR

• Input Type: Non-Inverting
• Number Of Outputs: 12
• On-state Resistance: 20 mOhm
• Current - Output / Channel: 25A
• Current - Peak Output: 35A
• Voltage - Supply: 5 V ~ 12 V
• Operating Temperature: 0°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 56-VQFN
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant

The turn off of the MOSFET is fundamentally the same as
the turn on in reverse order (Figure 36). V
level required to maintain the drain current (beginning of t4).
At that point, V
Where:
Crss = Transfer Capacitance
V
dv/dt value during this period, V
bus voltage for a short period of time. This overshoot is from
the inductive voltage kickback of the choke inductance and
parasitics of the traces. When V
voltage, C
decay at the rate of:
Eventually, the current reaches zero and the switching event
ends.
Efficiency of the MOSFETs
The equations below provide a rough estimate for power
dissipation of the upper and lower MOSFETs. These
equations do not take into account the reverse-recovery of
the lower MOSFETs body diode or a snubber circuit used in
this regard.
dI
-------- -
dV
-------------- -
P
P
DS
dt
LOWER
dt
UPPER
D
DS
eventually reaches the rail voltage. Because of the high
=
=
gm
gm
DG
FIGURE 36. MOSFET TURN OFF CURVES
=



=
V
-----------------------
R
Io
---------------------------------------------------------- -
V
-----------------------
plateau
Io
------------------------------------------------------------------------------ -
R
G
is fully discharged. The drain current starts to
plateau
2
G
2
DS
C
×
C
×
iss
Rds on
rss
Rds on
begins to rise at a rate of:



Vin
(
(
Vin
)
)
×
×
Vout
(
Vin Vout
23
DS
DS
–
+
Io
------------------------------------------------------------
often will rise beyond the
first reaches the rail
2
×
)
Vin
GS
×
2
Tsw
reduces to the
×
Fsw
(EQ. 11)
(EQ. 12)
(EQ. 10)
(EQ. 13)
ISL6580
Pupper = Power loss in upper MOSFET
Plower = Power loss in lower MOSFET
Io = Average Current
Rds(on) = On resistance for the particular MOSFET at the
appropriate gate voltage and temperature of operation
V
V
Fsw = Frequency of operation per phase
Tsw = On/Off Switch Time
Junction Temperature Evaluation
With power loss in a transistor comes dissipation of that
power in the form of heat. The higher the power loss, the
higher the parts junction temperature will be. A basic thermal
model is seen in Figure 37. Through the data of the
MOSFET used, the thermal resistivity from junction to case
can be determined. With a measurement of the case of the
MOSFET during operation, the FETs junction temperature
can be calculated.
The formula used for calculating junction temperature is:
T
P
* current through the device (I
R
This value can be found by using data sheets for the
individual transistors as well as thermal resistance data of
the specific package.
T
If the junction temperature rises above specification, the
transistor could fail. Also, high junction temperatures during
operation can cause reliability issues. In the same sense, if
the junction temperature difference between on and ambient
off conditions is significant, temperature cycling can be a
reliability issue as well.
Effective heat flux from the power transistor to ambient is
critical to ensure reliability. The main trade-off for effective
J
c
OUT
IN
D
θ
JC
= P
= Case Temperature
=Power dissipation = voltage across the transistor (V
= Input Voltage
= 10µs pulse rated junction to case thermal resistance.
= Output Voltage
D
FIGURE 37. THERMAL RESISTIVITY MODELING
*R
θ
JC
+T
C
REFERENCE TEMPERATURE
D
)
DS
)