3 Experimental Setup and Discussion

The setup for the experiments performed in this application note is comprised of a high-amperage current load in series with the devices under test, and necessary power supplies to drive the load. Figure 3-1 shows a rendering of the board used. From the diagram, note that for each test, all five samples for a given board weight or polygon size were run simultaneously, in series such that all boards can see the same current.

Figure 3-1 TMCS1123EVM, Busbar Configuration

Labview was employed to automate the process, as thermal equilibrium was time consuming to make sure true thermal equilibrium between points. The following steps were performed on each board to capture the below curves:

1. Power on all loads and necessary supplies to energize the test loop.
2. Create a current flow in the DUTs, beginning at 0A, and stepping in increments of 5As per step.
3. Temperature measurements are made in 1 second intervals. Current remains at the given level until residual temperature between measurements is less than 100m°C.
4. Move the next 5A current interval, and repeat steps 2 and 3.
5. Repeat steps 2-4 until one device registers 150°C
6. Reduce the step interval to 250mA per step, building from the largest step achieved in the previous process.
7. Temperature measurements are made in 1 second intervals. Current remains at the given step until residual temperature between measurements is less than 100m°C.
8. Repeat steps 5 and 6 until the first device reaches 165°C
9. Shut down all supplies and deenergize the test loop.

Note that while the same topology of the EVM was used, the addition of series busbars effectively changes the impedance profile of the board, and also creates local heat signatures on the total EVM. This resulted in a reduction of total load each device can manage, but allowed for streamline testing over the full current range. Another observation made during these tests is that thermal efficiency in the connections of the lugs and busbars is paramount, as well as copper plane integrity. Care needs to be taken to make sure that copper is not damaged during assembly, and that connections are tight to make sure as little thermal resistance as possible.