37.2.2 Junction Temperature

The average chip-junction temperature, TJ, in °C can be obtained from the following:

  1. TJ = TA + (PD x θJA)
  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 if a cooling device is necessary or not. If a cooling device has to be fitted on the chip, the second equation should be used to compute the resulting average chip-junction temperature TJ in °C.