This tool calculates the junction temperature of a LDO regulator
Formula
TJ = TA + (RθJA × PD )
where
- TA is the ambient temperature
- RθJA is the Junction-to-ambient thermal resistance
- PD is the power dissipation
PD = (VIN – VOUT) * IOUT + VIN * IQ
The power dissipation is calculated using the following quantities:
- Input Voltage VIN
- Output Voltage VOUT
- Output Current IOUT
- Quiescent (or Ground) Current IQ
Background
The larger the voltage difference between the input and output, the greater the power dissipation. The temperature is directly proportional to both the Junction-to-ambient thermal resistance and the power dissipation.
Example Calculation
For an input voltage of 5V and regulated output 3.3V, with the output current of 150 mA, Junction-to-ambient thermal resistance of 205 °C/W, the power dissipation is 256 mW and the junction temperature is 77.5 °C.