2022.03.09

Points of this article

・There are two methods for estimating T_{J}: using T_{A} and θ_{JA}, or using T_{T} and Ψ_{JT}.

・In both calculations, the IC power consumption P is necessary.

Up till now, to facilitate understanding of thermal resistance data, we have explained how θ_{JA} and Ψ_{JT} are used, or can be used, in calculations to estimate T_{J}, and have discussed the characteristics of Ψ_{JT} and the usefulness of θ_{JA} and Ψ_{JT} in estimating T_{J}. From here, we will present examples of calculations to estimate T_{J} using thermal resistance data.

We begin with the basic calculation equations used in estimation of T_{J}. T_{J} can be estimated using either of the following two equations.

① Using the ambient temperature T_{A}

② Using the temperature T_{T} at the center of the top surface of the IC package in the state of actual use

Whichever equation is used, the power consumption P is essentially the product of the power supply voltage and the power supply current for the IC, but the IC functions (whether it is a power supply IC, an op-amp, etc.), the output load current, and other factors must be considered. In all cases, however, the power consumption is determined from the current and voltage consumed by the IC. Shown below is an example of a linear regulator.

This is the simplest example; the power consumption of the IC itself is V_{IN}×I_{CC}, the power consumption of the load is the input/output difference (V_{IN}-V_{OUT}) ×I_{OUT}, and the sum of the two is the power consumption for the IC as a whole.

From the next article, examples are used in actual determination of T_{J}.

Downloadable materials, including lecture materials from ROHM-sponsored seminars and a selection guide for DC-DC converters, are now available.

- About Thermal Design
- Changes in Engineering Trends and Thermal Design
- A Mutual Understanding of Thermal Design
- Fundamentals of Thermal Resistance and Heat Dissipation: Heat Transmission and Heat Dissipation Paths
- Fundamentals of Thermal Resistance and Heat Dissipation: About Thermal Resistance
- Fundamentals of Thermal Resistance and Heat Dissipation : Thermal Resistance in Conduction
- Fundamentals of Thermal Resistance and Heat Dissipation : Thermal Resistance in Convection
- Fundamentals of Thermal Resistance and Heat Dissipation : Thermal Resistance in Emission
- Thermal Resistance Data: JEDEC Standards, Thermal Resistance Measurement Environments, and Circuit Boards
- Thermal Resistance Data: Actual Data Example
- Thermal Resistance Data: Definitions of Thermal Resistance, Thermal Characterization Parameters
- Thermal Resistance Data: θJA and ΨJT in Estimation of TJ: Part 1
- Thermal Resistance Data: θJA and ΨJT in Estimation of TJ: Part 2
- Estimating TJ: Calculation Example Using θJA
- Estimating TJ: Calculation Example Using ΨJT
- Estimating TJ: Calculation Example Using Transient Thermal Resistance
- Estimation of Heat Dissipation Area in Surface Mounting and Points to be Noted
- Surface Temperature Measurements: Thermocouple Types