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Estimating TJ: Basic Calculation Equations
2022.03.09
Points of this article
・There are two methods for estimating TJ: using TA and θJA, or using TT and ΨJT.
・In both calculations, the IC power consumption P is necessary.
Up till now, to facilitate understanding of thermal resistance data, we have explained how θJA and ΨJT are used, or can be used, in calculations to estimate TJ, and have discussed the characteristics of ΨJT and the usefulness of θJA and ΨJT in estimating TJ. From here, we will present examples of calculations to estimate TJ using thermal resistance data.
Basic Calculation Equations Used in Estimation of TJ
We begin with the basic calculation equations used in estimation of TJ. TJ can be estimated using either of the following two equations.
① Using the ambient temperature TA
② Using the temperature TT 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 VIN×ICC, the power consumption of the load is the input/output difference (VIN-VOUT) ×IOUT, 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 TJ.
【Download Documents】 Thermal Design of Semiconductor Components in Electronics
Thermal design has become a new issue in the design of electronic equipment in recent years, as thermal countermeasures have been the focus of attention. Although heat has been an important consideration for some time, the requirements for electronic equipment have changed in recent years, making it necessary to review conventional thermal countermeasures. This handbook describes thermal design based on the assumption that ICs and transistors are basically used in electronic equipment.
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Electrical Circuit Design
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Basic Alternating Current (AC)
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- Fundamentals of Thermal Resistance and Heat Dissipation: Heat Transmission and Heat Dissipation Paths
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- Thermal Resistance Data: JEDEC Standards, Thermal Resistance Measurement Environments, and Circuit Boards
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- Thermal Resistance Data: θJA and ΨJT in Estimation of TJ: Part 1
- Thermal Resistance Data: θJA and ΨJT in Estimation of TJ: Part 2
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- Surface Temperature Measurements: Thermocouple Mounting Position
- Surface Temperature Measurements: Treatment of Thermocouple Tips
- Surface Temperature Measurements: Influence of the Thermocouple
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- Estimating TJ: Calculation Example Using θJA
- Estimating TJ: Calculation Example Using ΨJT
- Estimating TJ: Calculation Example Using Transient Thermal Resistance
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Foundations of Electronic Circuit Simulation Introduction
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