4 Application-Specific Use Cases

One important question to address in many applications is the maximum ambient temperature (T_{A_MAX}) the application can run. As discussed earlier, the following equation applies:

T_{A_MAX} = T_{J_Limit} – R_J-A x P_TOT

Where:

• T_{J_Limit} is provided in the device data sheet, for example 105°C for industrial parts.
• R_J-A depends on the application hardware: PCB design, presence or absence of heatsink, presence or absence of air flow, enclosure, etc.
• P_TOT represents the application activity and is largely influenced by the software run by the processor.

As a rule of thumb, for applications requiring T_{A_MAX} lower than 60°C, the SAMA7G54 junction temperature remains below the 105°C limit. For T_{A_MAX} greater than 60°C, the operating junction temperature verification is required during the prototyping phase to ensure that the 105°C limit is not exceeded. Measuring the junction temperature is also a way to estimate more accurately the device lifetime in real conditions. Refer to the “SAMA7G5 Series Product Lifetime Estimation” application note (see Reference Documents).

In this section, simulated curves show the impact of various parameters (R_J-A, P_TOT, time) on the device junction temperature and power dissipation.