When searching for a valid inductor cross-reference, an engineer typically utilizes two different resources: parametric search on distributor websites or manufacturer cross-reference tools. The disadvantages of using manufacturer cross-reference tools are that they are limited to results from one manufacturer and that they are often outdated and limited in scope. Using parametric search on distributor websites expands the results to all manufacturers, but it is a much more time-consuming process to validate the results. In an ideal world, an engineer could have the speed and reliability of a manufacturer cross-reference tool as well as the up-to-date data and product range of the distributors. In this article, we will look at two popular series of inductors from Würth Electronics and Murata, show the traditional method of cross-referencing, introduce a technique to add reliability to this method, and finally introduce a tool which can present reliable and valid inductor cross-references at lightning speed.
<h2> Comparing Datasheet Values of Fixed Inductors </h2>
The first step in finding a valid replacement or back-up inductor for a design is comparing the datasheet parameters. Here we will compare an inductor from Würth’s WE-LQS 5040 (more generally, WE-LQS) series of semi-shielded SMD inductors to Murata’s LQH5BPN (also seen sometimes as LQH or LQH5BPN_38). For this example, we will look for both electrical and mechanical compatibility, which is the typical requirement if the design of the product has already been completed and no additional redesign is possible.
The two inductors we will look at in this article are the Würth 74404054220 (WE-LQS 5040 Series) and the Murata LQH5BPN220M38 (LQH5BPN Series). These inductors are typically used in DC/DC converter applications. First, we will look at the mechanical dimensions. Both parts have square footprints; the Würth part has sides of 5mm (tolerance of 0.2mm) while the Murata part has sides of 4.9mm (also tolerance of 0.2mm). Both parts have a maximum height of 4mm. The differences in mechanical dimensions are small enough for the parts to be compatible in most consumer electronics design scenarios.
Next, we will examine the electrical parameters. Both parts have a nominal inductance of 22uH at 100kHz and a rated current of 1.5A causing a temperature rise of 40 degrees. In DC resistance the parts are very similar, with the Würth part advertising 129mOhms and the Murata part 132mOhms, a negligible difference when tolerances are considered. Speaking of tolerance, both have a tolerance on the nominal inductance of 20%. Both inductors are semi-shielded (at some distributors the Murata part is listed as shielded) and the Murata part promises a 30% inductance drop at 1.6A, the Würth part at 1.7A.
From looking at the electrical and mechanical datasheet parameters of both parts, we can see that they appear to be compatible in both aspects. This is where a typical cross-reference ends with the conclusion that the two parts could be compatible with each other. This analysis does not, however, confirm with 100% certainty that these two parts will work in place of one another.
<h2> Operating Point Analysis of Fixed Inductors </h2>
A comparison of datasheet values is a good starting point for cross-referencing, but it does not answer one important question: How do these parts perform at the operating current and frequency at which they will be used? In the past, this type of analysis has been extremely time consuming or simply ignored, since the operating point behavior of parts needed to be measured manually or (if you’re lucky) found on the manufacturer’s website. If these characteristic charts are available for each part, the two graphs must be compared by eye, which is challenging considering the different scales and measurement conditions used by different manufacturers.
Today, operating point analysis can be done simply, and for free, using the chart comparison tools at SourcingBot. Their engineers have collected and compared lab-measured data for fixed inductors and other passive components so that they can be easily compared across datasheet values and operating points. If we search for our two inductors in their database, we can easily check the impedance and inductance against frequency, as well as the saturation and temperature rise curves. This is where we can verify if our two inductors will perform the same at our intended operating point.
Here we can see that the two inductors have very similar saturation behavior, but not equal. Both parts exceed their datasheet ratings, with the Würth part keeping the rated inductance at lower currents but dropping off faster than the Murata part. In a sensitive or high-current application, this difference could be critical.
Next, let’s look at the temperature curves for these two parts. Here we can see that the Murata inductor is hotter at a given current value than the Würth part. Inductors are often critical heat-generators in DC/DC converters, so this often needs to be accounted for. With a simple datasheet comparison, this difference would be missed.
<h2> Automating the Inductor Cross-Referencing Process with SourcingBot </h2>
In this article, we have seen that all cross-references are not made equal. At certain operating points, the two inductors do not perform the same, meaning that deeper analysis is required to guarantee compatibility. This entire process has been automated by the engineers at SourcingBot to speed up your product development and strengthen your supply chain. Their website automatically performs the first step of cross-referencing, the datasheet comparison, and presents a list of the most similar parts.
Depending on the requirement of your cross-reference different parts can be found, for example, those with higher rated current, at the click of a button. Within the comparison table, it is simple to compare the performance at your operating point with their “Click to Compare” button. In addition, lab-measured parameters are compared to the datasheet parameters in an easy-to-read table for each part.
To try the SourcingBot cross-referencing and comparison tools, visit their website at sourcingbot.com and start finding parts!