19 of 48 October 3, 2011
IDT 89HPES48H12 Data Sheet
Thermal Considerations
This section describes thermal considerations for the PES48H12 (35mm
2
FCBGA1156 package). The data in Table 17 below contains information
that is relevant to the thermal performance of the PES48H12 switch.
Note: It is important for the reliability of this device in any user environment that the junction temperature not exceed the T
J(max)
value
specified in Table 17. Consequently, the effective junction to ambient thermal resistance (
θ
JA
) for the worst case scenario must be
maintained below the value determined by the formula:
θ
JA
= (T
J(max)
- T
A(max)
)/P
Given that the values of T
J(max)
, T
A(max)
, and P are known, the value of desired θ
JA
becomes a known entity to the system designer. How to
achieve the desired
θ
JA
is left up to the board or system designer, but in general, it can be achieved by adding the effects of θ
JC
(value
provided in Table 17), thermal resistance of the chosen adhesive (
θ
CS
), that of the heat sink (θ
SA
), amount of airflow, and properties of the
circuit board (number of layers and size of the board). As a general guideline, this device will not need a heat sink if the board has 10 or
more layers AND the board size is larger than 4"x12" AND airflow in excess of 1 m/s is available. It is strongly recommended that users
perform their own thermal analysis for their own board and system design scenarios.
Symbol Parameter Value Units Conditions
T
J(max)
Junction Temperature 125
o
C Maximum
T
A(max)
Ambient Temperature 70
o
C Maximum for commercial-rated products
θ
JA(effective)
Effective Thermal Resistance, Junction-to-Ambient
12.6
o
C/W Zero air flow
6.4
o
C/W 1 m/S air flow
5.4
o
C/W 2 m/S air flow
θ
JB
Thermal Resistance, Junction-to-Board 2.1
o
C/W
θ
JC
Thermal Resistance, Junction-to-Case 0.1
o
C/W
P Power Dissipation of the Device 6.82 Watts Maximum
Table 17 Thermal Specifications for PES48H12, 35x35mm FCBGA1156 Package
