The average chip-junction temperature, T_{J}, in °C, can be obtained from the following
equations:

**Equation 1**: T_{J}= T_{A}+ (P_{D}x θ_{JA})**Equation 2**: T_{J}= T_{A}+ (P_{D}x (θ_{HEATSINK}+ θ_{JC}))

where:

- θ
_{JA}= Package thermal resistance, Junction-to-ambient (°C/W), see Table 1 - θ
_{JC}= Package thermal resistance, Junction-to-case thermal resistance (°C/W), see Table 1 - θ
_{HEATSINK}= Thermal resistance (°C/W) specification of the external cooling device - P
_{D}= Device power consumption (W) - T
_{A}= Ambient temperature (°C)

From the first equation, the user can derive the estimated
lifetime of the chip and decide whether a cooling device is necessary or not. If a
cooling device has to be fitted on the chip, the second equation must be used to compute
the resulting average chip-junction temperature T_{J} in °C.

Power usage can be calculated by adding together system power consumption and I/O module power consumption. The current drawn from pins with a capacitive load may be estimated (for one pin) as follows:

I_{cp} ≈ V_{DD} * C_{load} * f_{sw}

Where C_{load} = pin load capacitance and f_{sw} = average switching
frequency of I/O pin.