Thermal Calculator — InnovChip

Thermal Calculator

Compute junction temperature from power dissipation and thermal resistance, and find the maximum safe dissipation for a package.

Calculator

About This Calculator

Junction temperature is the fundamental reliability limit for silicon. With the package's thermal resistance θJA (°C/W) and the ambient temperature, junction temperature is Tj = Ta + P·θJA. This tool computes Tj, the max dissipation the package can handle before hitting your junction limit, and the remaining margin.

How to Use

  1. Enter the total power the package must dissipate (I²R, switching losses, etc.).
  2. Set θJA from the datasheet — note it changes drastically with PCB copper and airflow.
  3. Enter ambient and the datasheet max junction (typically 125-150 °C).
  4. Read Tj and margin; if 'Within Safe Limits' is 0, add heatsinking, airflow, or reduce power.

Formulas

Junction temperatureTj = Ta + P × θJA
Max dissipationP(max) = (Tj(max) − Ta) / θJA
MarginMargin = Tj(max) − Tj

Design Notes

θJA is a PCB-dependent figure; a 1 oz 30×30 mm board can halve θJA versus a small breakout.

For pulsed loads use the transient thermal impedance curves (Zθ) instead of steady θJA.