ISL59533 Datasheet, PDF (23/24 Pages) Intersil Corporation – 32x32 Video Crosspoint with Differential Inputs

ISL59533
Power Dissipation and Thermal Resistance
With a large number of switches, it is possible to exceed the
150°C absolute maximum junction temperature under
certain load current conditions. Therefore, it is important to
calculate the maximum junction temperature for an
application to determine if load conditions or package types
need to be modified to assure operation of the crosspoint
switch in a safe operating area.
The maximum power dissipation allowed in a package is
determined according to:
PD_MAX
=
T_{----J---M-----A----X-----–-----}T_{----A---M-----A----X--}
Θ_JA
Where:
• T_JMAX = Maximum junction temperature = 125°C
• T_AMAX = Maximum ambient temperature = 85°C
• θ_JA = Thermal resistance of the package
The maximum power dissipation actually produced by an IC
is the total quiescent supply current times the total power
supply voltage, plus the power in the IC due to the load, or:
n
∑ ^{P D}M A X
=
V_S
×
I_SMAX
+
i
=
1
(V_S
–
V_OUTi)
×
V_{-----O----U----T----i}
R_Li
Where:
• V_S = Supply voltage = 5V
• I_SMAX = Maximum quiescent supply current = 700mA
• V_OUT = Maximum output voltage of the application = 2V
• R_LOAD = Load resistance tied to ground = 150
• n = 1 to 32 channels
n
∑ ^{P D} M A X
=
V_S
×
I_SMAX
+
i
=
(V_S
1
–
V_OUTi)
×
V_{-----O----U----T----i =}
R_Li
4.8 W
The reqired θ_JA to dissipate 4.8W is:
Θ_JA
=
T_{----J---M-----A----X-----–-----}T_{----A---M-----A----X-- =}
PD_MAX
8.33 ( ° C /W )
Table 8 shows θ_JA thermal resistance results with a
Wakefield heatsink and without heatsink and various airflow.
At the thermal resistance equation shows, the required
thermal resistance depends on the maximum ambient
temperature.
TABLE 8. θ_JA THERMAL RESISTANCE [°C/W]
Airflow [LFM]
0
250
500
750
No Heatsink
18
14.3
13.0
12.6
Wakefield
16.0
7.0
6.0
4.7
658-25AB
All Intersil U.S. products are manufactured, assembled and tested utilizing ISO9000 quality systems.
Intersil Corporation’s quality certifications can be viewed at www.intersil.com/design/quality
Intersil products are sold by description only. Intersil Corporation reserves the right to make changes in circuit design, software and/or specifications at any time without
notice. Accordingly, the reader is cautioned to verify that data sheets are current before placing orders. Information furnished by Intersil is believed to be accurate and
reliable. However, no responsibility is assumed by Intersil or its subsidiaries for its use; nor for any infringements of patents or other rights of third parties which may result
from its use. No license is granted by implication or otherwise under any patent or patent rights of Intersil or its subsidiaries.
For information regarding Intersil Corporation and its products, see www.intersil.com
23
FN6222.0
March 13, 2006