82P33714_17 Datasheet, PDF (44/64 Pages) Integrated Device Technology – Synchronous Equipment Timing Source for Synchronous Ethernet

82P33714 Datasheet
7
THERMAL MANAGEMENT
The device operates over the industry temperature range -40°C ~
+85°C. To ensure the functionality and reliability of the device, the maxi-
mum junction temperature T_jmax should not exceed 125°C. In some
applications, the device will consume more power and a thermal solution
should be provided to ensure the junction temperature T_j does not
exceed the T_jmax.
7.1 JUNCTION TEMPERATURE
Junction temperature T_j is the temperature of package typically at the
geographical center of the chip where the device's electrical circuits are.
It can be calculated as follows:
Equation 1: T_j = T_A + P X _JA
Where:
_JA = Junction-to-Ambient Thermal Resistance of the Package
T_j = Junction Temperature
T_A = Ambient Temperature
P = Device Power Consumption
In order to calculate junction temperature, an appropriate _JA must
be used. The _JA is shown in Table 18:
Table 18 has the thermal results based on JEDEC standard condi-
tions. It is industry practice and IDT practice to publish these results.
If the PCB design differs from the JEDEC standard conditions, then
the thermal results will be different.
7.2 THERMAL RELEASE PATH
In order to maximize both the removal of heat from the package,
electrical grounding from the package to the board can be done through
thermal vias to effectively conduct from the surface of the PCB to the
ground plane(s). The vias act as “heat pipes”. The number of vias (i.e.
“heat pipes”) are application specific and dependent upon the package
power dissipation as well as electrical conductivity requirements. Thus,
thermal and electrical analysis and/or testing are recommended to
determine the minimum number needed. It is recommended to use as
many vias connected to ground as possible. It is also recommended that
the via diameter should be 12 to 13mils (0.30 to 0.33mm) with 1oz cop-
per via barrel plating. These recommendations are to be used as a
guideline only.
Table 18: Thermal Data
Parameter
Thermal Resistance
Symbol
_JC
_JB
_JA1
_JA2
_JA3
_JA4
CONDITIONS
Junction to Case
Junction to Base
Junction to Air, still air
Junction to Air, 1 m/s air flow
Junction to Air, 2 m/s air flow
Junction to Air, 3 m/s air flow
PKG
QFN/NLG72
Typ Values (^oC/W)
11.2
0.42
20.75
17.05
15.66
14.96
Notes
JEDEC PCB (7x7 matrix)
©2017 Integrated Device Technology, Inc.
44
Revision 6, January 23, 2017