FAQ Issue 5: How to determine the resistance change of thin film resistors after "drift"? Here's a good way!

Latest update time：2021-08-12

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Introduction

During the use of thin film resistors, as the working time increases, the resistance value of the resistor will drift, which will affect the performance of the entire circuit system. In order to determine the tolerance of electronic products throughout the life cycle, sometimes we want to have an accurate estimate of the drift change of the thin film resistor value in the "worst case". Today we will share with you a quick and accurate calculation method.

ask

How to calculate or estimate the worst-case drift change of film resistance value based on the operating time of the film?

The drift (aging) of a resistor can be estimated using the Arrhenius equation . For example, you can find a table of "Maximum resistance change at rated dissipation" on page 2 of the Vishay TNPW e3 datasheet.

(Click to enlarge the image)

As shown in the figure above, the maximum percentage change in resistance value varies with different operating modes.

Using the Arrhenius equation given below, customers can estimate the resistance drift based on the specified resistance change shown in the datasheet:

To illustrate this with an example - assuming 15,000 hours of operation in the application, the drift can be estimated as follows:

The parameters from the datasheet (standard operating mode) are as follows - requiring 15,000 hours of operation at P70, so full load at 70°C ambient temperature:

The drift of the resistor value can be estimated as follows:

If a customer wishes to calculate the lifetime tolerance of an end product using a worst-case resistance change rate, they are adding together all possible changes in their design—even though the actual resistance change may be lower.

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