The average chip-junction temperature, TJ, in °C can be obtained from the following
equations:
- Equation 1- TJ = TA + (PD x θJA)
- Equation 2 - TJ = TA + (PD x (θHEATSINK + θJC))
where:
- θJA = Package thermal resistance,
Junction-to-ambient (°C/W), see Thermal Resistance Data
- θJC = Package thermal resistance,
Junction-to-case thermal resistance (°C/W), see Thermal Resistance Data
- θHEATSINK = Thermal resistance (°C/W)
specification of the external cooling device
- 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 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 TJ in °C.