IDT82P20416
16-CHANNEL SHORT HAUL T1/E1/J1 LINE INTERFACE UNIT
Thermal Management
97
December 17, 2009
7
THERMAL MANAGEMENT
The device is designed to operate over the industry temperature
range -40°C ~ +85°C. To ensure the functionality and reliability of the
device, the maximum junction temperature, Tjmax, 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
Tj does not exceed Tjmax. Below is a table listing thermal data for the
IDT82P20416.
7.1
JUNCTION TEMPERATURE
Junction temperature Tj 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:
Tj = TA + P * θJA
Where:
θJA = Junction-to-Ambient Thermal Resistance of the package
Tj = Junction Temperature
TA = Ambient Temperature
P = Device Power Consumption
For the IDT82P20416, the above values are:
θJA = 23.7 °C/W (when airflow rate is 0 m/s. See the above table )
Tjmax = 125 °C
TA = - 40 °C ~ 85 °C
7.2
EXAMPLE OF JUNCTION TEMPERATURE CAL-
CULATION
Assume:
TA = 85 °C
θJA = 23.7 °C/W (airflow: 0 m/s)
P = 1.46 W (E1 120
, 100% ones, External Impedance matching)
The junction temperature Tj can be calculated as follows:
Tj = TA + P * θJA = 85 °C + 1.46 W X 23.7 °C/W = 119.6 °C
The junction temperature of 119.6 °C is below the maximum junction
temperature of 125 °C, so no extra heat enhancement is required.
In some operation environments, the calculated junction temperature
might exceed the maximum junction temperature of 125 °C and an
external thermal solution such as a heatsink is required.
7.3
HEATSINK EVALUATION
A heatsink is expanding the surface area of the device to which it is
attached.
θJA is now a combination of device case and heatsink thermal
resistance, as the heat flowing from the die junction to ambient goes
through the package and the heatsink.
θJA can be calculated as follows:
Equation 2:
θJA = θJC + θHA
Where:
θJC = Junction-to-Case (heatsink) Thermal Resistance
θHA = Heatsink-to-Ambient Thermal Resistance
For the IDT82P20416,
θJC is 4.2 °C/W.
θHA determines which heatsink can be selected to ensure the junc-
tion temperature does not exceed Tjmax. According to Equation 1 and 2,
the heatsink-to-ambient thermal resistance
θHA can be calculated as
follows:
Equation 3:
θHA = (Tj - TA) / P - θJC
Assume:
Tj = 125 °C (Tjmax)
TA = 85 °C
P = 2.72 W (E1 75
, 100% ones, Fully Internal Impedance matching)
θJC = 4.2 °C/W
The Heatsink-to-Ambient thermal resistance
θHA can be calculated
as follows:
θHA = (125 °C - 85 °C ) / 2.72 W - 4.2 °C/W = 10.51°C/W
That is, if a heatsink whose heatsink-to-ambient thermal resistance
θHA is below or equal to 10.51 °C/W is used in such operation environ-
ment, the junction temperature will not exceed the maximum junction
temperature.
Package
θJC (°C/W) 1 θJB (°C/W) 2 θJA (°C/W) 3 Airflow (m/s)
484-pin BF
4.2
5.3
23.7
0
18.7
1
17.0
2
16.1
3
15.5
4
15.0
5
Note:
1. Junction-to-Case Thermal Resistance
2. Junction-to-Board Thermal Resistance
3. Junction-to-Ambient Thermal Resistance