The average chip-junction temperature, TJ, in °C can be obtained from the
following:
- 1.TD = TA + (PD x θJA)
- 2.TD = TA + (PD x (θHEATSINK +
θJC))
where:
- θJA = package thermal resistance,
Junction-to-ambient (°C/W), provided in Table 1
- θJC = package thermal resistance,
Junction-to-case thermal resistance (°C/W), provided in Table 1
- θHEATSINK = cooling device thermal resistance (°C/W), provided in the
device datasheet
- PD = device power consumption (W)
- TA = ambient temperature (°C)
From the first equation, the user can derive the estimated lifetime of the chip and
decide if a cooling device is necessary or not. If a cooling device is to be fitted on
the chip, the second equation should be used to compute the resulting average
chip-junction temperature TJ in °C.