This tool calculates the junction temperature of a LDO regulator

**Formula**

**T _{J} = T_{A} + (R_{θJA} × P_{D} )**

where

**T**is the ambient temperature_{A}**R**is the Junction-to-ambient thermal resistance_{θJA}**P**is the power dissipation_{D}

**P _{D} = (V_{IN} – V_{OUT}) * I_{OUT} + V_{IN} * I_{Q}**

The power dissipation is calculated using the following quantities:

- Input Voltage
**V**_{IN} - Output Voltage
**V**_{OUT} - Output Current
**I**_{OUT} - Quiescent (or Ground) Current
**I**_{Q}

**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.