Power Dissipation vs Die Temp

A calculator for estimating junction temperature from power dissipation and packaging/heatsink characteristics.

Instructions | Troubleshooting
Parameters

TA Ambient temp. ªC
V+ Pos. supply V
V- Neg. supply V
IQ Quiescent curr. mA
VOUT Load voltage V
RL Load resistance ohms
VGND Load ground V
ThetaJA Theta ªC / W



Instructions

This calculator computes die power dissipation and temperature for a linearly regulated output from quantities specified under "Parameters". It also computes power dissipated in an external load.

The model is of a linear push-pull output driving an external resistive load. Two common examples would be a digital bipolar output or a Class A amplifier. The voltage across the resistor, VOUT-VGND determines the current, IL, supplied by the output, which requires the internal driver dissipate IL * (V+-VOUT) or IL * (VOUT-V-) to supply the current linearly. Which rail supplies the current depends on whether the load current is positive or negative.

Total on-chip power, PTOTAL, is the sum of the power dissipated driving the load, plus the quiescent power, IQ * (V+-V-). The on-chip rise is equal to TA + thetaJA*PTOTAL. ThetaJA = ThetaJP (junction-to-package) + ThetaPA (package-to-ambient).

To use this calculator, simply enter the appropriate quantities in the parameter fields and then click "Calculate" or tab from field to field.


Troubleshooting

No special problems are known to exist with this calculator at this time.

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Additional Resources

Mini Tutorials
  • MT-093: Thermal Design Basics (pdf)