The longest thermal time constants of device packaging and PCBs are in the order of seconds; therefore, any continuous DC or sinusoidal AC periodic waveform with a frequency higher than 1 Hz can be evaluated based on the RMS continuous-current level. The continuous-current capability has a strong dependence upon the operating ambient temperature range expected in operation. Figure 8-5 shows the maximum continuous current-handling capability of the device on the TMCS1100EVM. Current capability falls off at higher ambient temperatures because of the reduced thermal transfer from junction-to-ambient and increased power dissipation in the leadframe. By improving the thermal design of an application, the SOA can be extended to higher currents at elevated temperatures. Using larger and heavier copper power planes, providing air flow over the board, or adding heat sinking structures to the area of the device can all improve thermal performance.

Figure 8-5 Maximum Continuous RMS Current vs. Ambient Temperature