Tuesday, March 16, 2010

Basic Thermal Equation and Heat Transfer

Thermal Equation Parameters
Many parameters contribute to a design's thermal circuit, including the
device's maximum power consumption for the design, the maximum
environment temperature, package characteristics, and airflow at the

Maximum Power Consumption (P)
Use the power calculator values from design simulations in the Altera
Quartus® II software (or the device's power calculator at
http://www.altera.com) to estimate the maximum power consumption
of the device. Once a prototype design is available, measure the actual
power consumption and use this value for thermal calculations.
Maximum Temperature (TJ & TA)

The maximum ambient and junction temperatures are found in the data
sheet for the device under Device Absolute Maximum Rating and the
operating junction temperature is found under Device Recommended
Operating Conditions. The temperature must be kept within the
maximum conditions or damage could occur. The junction temperature
should be kept within the recommended operating conditions to ensure
the device achieves the performance reported by the Quartus II software.

The rate at which heat is conducted
through a material is proportional
to the area normal to the heat flow
and to the temperature gradient
along the heat flow path. For a one
dimensional, steady state heat flow
the rate is expressed by Fourier’s

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