Steve Edwards*, an experienced analog design engineer, has written several calculators to automate repetitive tasks. These tools are being shared to help other analog design engineers who select, specify, and characterize analog circuits. We will summarize the functionality of one such tool, the Package Thermal Analysis Calculator.
The Package Thermal Analysis (PTA) is a program written for the HP50g calculator that aids in the analysis of the thermal properties of integrated circuit packages. These include thermal resistance, power dissipation and derating, and die, package, and ambient temperatures. PTA can find any of these parameters given the others. PTA can be run on a PC using the free program HPUserEdit 5.4, found at www.hpcalc.org, or our calculator page.
Ten parameters are used.
PTA allows ten parameters to be entered (P, Tj, θjc, Tc, θca, Ta, θja, DF, Tjmax, and Pmax), and nine found (P, Tj, θjc, Tc, θca, Ta, θja, DF, and Pmax) as a function of the other parameters.
These parameters appear in PTA as shown below:
When power is generated within a die, heat is produced that flows toward the lower temperature of the surrounding air. The heat must travel via the molding compound, bond wires, leads, and (in some devices) an exposed leadframe pad. The inability of the package to immediately dissipate the heat results in a rise in die (Tj) and package (Tc) temperatures. The thermal resistance (θjc + θca), and therefore the path taken by the heat, varies with the package construction, and PCB mounting. For example,
The calculator user's guide tutorial details the types of integrated circuit packages thermals and how it is calculated. The practical example uses PTA to estimate the package thermals of the MAX5112, 9-channel DAC in a laser optical driver. The example takes us from entering the data, through solving and finding package power vs. temperature.
*Steve Edwards is no longer with Maxim