Thermal path and heatsink
Steady series thermal path, measured-package PsiJT estimate, or user-supplied transient thermal impedance.
Development preview. Check the assumptions below before relying on a result. Calculations run in your browser.
How it calculates
Assumptions
- ThetaJA depends on board, airflow and mounting; the datasheet reference-board value is not a universal property.
- PsiJT is a characterization parameter used with measured package-top temperature, not a series thermal resistance and not a heatsink design parameter.
- Pulse mode uses absolute single-pulse Zth (K/W), logarithmic interpolation and an initially uniform junction temperature. Repetitive pulse superposition is not included.
Worked example
These are the calculator's default inputs. Change any input above to recalculate.
Inputs
- Thermal model
- heatsink
- Device power / pulse power
- 5 W
- Ambient / initial junction temperature
- 25 °C
- Maximum junction temperature
- 125 °C
- Junction-case resistance
- 2 K/W
- Case-sink resistance
- 0.5 K/W
- Sink-ambient resistance
- 10 K/W
- Assembly thetaJA
- 40 K/W
- Measured package-top temperature
- 65 °C
- PsiJT characterization parameter
- 1 K/W
- Pulse duration
- 0.01 s
- Zth time coordinates
- 0.001, 0.01, 0.1, 1, 10 s
- Absolute transient Zth coordinates
- 0.1, 0.5, 2, 10, 20 K/W
Results
- Estimated junction temperature
- 87.5 °C
- Maximum permissible sink resistance
- 17.5 K/W
- Thermal coefficient used
- 12.5 K/W
- Power at junction limit
- 8 W