CPC7524
INTEGRATED
C
IRCUITS
D
IVISION
higher switch current and/or higher ambient operating
temperatures will need to consider the thermal
performance.
When using the individual switches of the CPC7524
within their allowable operating region, no restrictions
are placed on any other switch.
Being a real physical device the CPC7524 has a finite
thermal capability that when properly considered will
ensure appropriate behavior and performance.
Determination of the thermal constraint is easily
accomplished using the following power equations:
PTOTAL = P
+ PSW
VDD
and
T
PTOTAL = ---------
JA
Where P
is the dissipated power drawn from the
VDD
V
supply and P
is the power dissipated by the
DD
SW
active switches. The V power can be calculated
DD
from the “VDD Voltage Supply Specifications” on
page 7 while the power dissipated by the switches is
the sum of the concurrent active switches. Total switch
power is the sum of the maximum current through
each active switch times the On-Resistance of the
2
switch (I
X R ).
ON
SWx
The second equation is used to calculate the
maximum ambient temperature that the device can be
operated in based on the calculated total power of the
previous equation. P
, the value obtained in the
TOTAL
first equation; T, the junction temperature rise of the
CPC7524 from ambient; and , the thermal
JA
impedance of the device package are used to
determine the maximum operating ambient
temperature.
Using the junction temperature rise equation
T = T - T ; the thermal impedance = 70C/W; and a
J
A
JA
maximum junction temperature T
reduces to:
= 110C, the equation
J-MAX
TA – MAX = TJ – MAX–PTOTAL JA
To avoid entering thermal shutdown, the value for the
maximum junction temperature was set to 110C.
Conversely, it is possible to rework the equations to
determine the maximum switch current for a maximum
ambient current.
R02
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