If you examine TDK’s MLCC Cross-Reference tool, you will find no suggested cross-references for Würth’s WCAP-CSGP series capacitors. This is often the case with manually assembled cross-reference lists, that many series are not considered or the list becomes out of date. In this article, we will be taking a closer look at the cross-reference criteria for these two series and a technique for quick validation and safe integration of automated cross-reference results into existing designs. First we will look at the two series from a simple cross-reference perspective, then we will make a more detailed analysis of performance at different operating points, and finally an automated cross-reference tool will be introduced.
Comparing Datasheet Values of Ceramic Capacitors
The first step in finding a valid replacement part for a ceramic capacitor is comparing the datasheet values. In this example, we will take a pair of capacitors, one from each series, and look at the electrical and mechanical parameters typically used when engineers create general part cross-references, like the ones seen in the TDK example at the top of the article.
The two capacitors which we will examine here are the Würth 885012206071 (WCAP-CSGP Series) and the TDK C1608X7R1E104K080AA (C Series). If the datasheet parameters are compared for these two products WCAP-CSGP and TDK, it appears that they are exactly the same. They share the same mechanical size/case code (0603), capacitance (100nF), voltage rating (25V), dielectric (X7R), and tolerance (10%). In addition, both are automotive rated and feature soft terminations. A typical cross-reference ends here with the conclusion that the parts are perfectly compatible between WCAP-CSGP and TDK. In the next section, we will take a more detailed approach and see if these two capacitors WCAP-CSGP and TDK are indeed identical.
Operating Point Analysis of Ceramic Capacitors
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 voltage 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 ceramic capacitors and other passive components so that they can be easily compared across datasheet values and operating points. If we search for our two capacitors, we can easily see the impedance and series resistance against frequency, as well as the change in capacitance against frequency. This is where we can verify if our two capacitors will perform the same at our intended operating point.
Here we can see the impedance behavior of the two capacitors at different frequencies. This chart tells us that the self-resonant frequency of the Würth part is about 10MHz higher than the TDK part. This could be a critical difference if the part is being used at around 15MHz, where the TDK part would be entering resonance behavior, while the Würth part would continue to operate as a capacitor.
Here is the equivalent series resistance (ESR) of the two capacitors against frequency. This shows that the TDK part has a lower ESR over most of the operational frequency range. This difference could be quite important in a high-efficiency design or one with strict thermal requirements.
Here the capacitance against voltage behavior is displayed. It can be seen that the TDK part retains more capacitance at the end of the rated voltage range. This difference may be critical in decoupling or filter applications. Depending on the operating point at which the capacitor will be used, these characteristic charts can inform you whether the two parts will perform to the required specifications.
Automating the Cross-Referencing Process with SourcingBot
In this article, we have seen that all cross-references are not made equal. Many cross-reference tools and PDFs do not contain information on all series from all manufacturers, and the information they do contain is not sufficient to validate a cross-reference at all operating points. While these capacitors could replace each other in many applications, there are certain operating points where the two capacitors 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. Within the comparison table, it is simple to compare the performance at your operating point with their “Click to Compare” button.
To try the SourcingBot cross-referencing and comparison tools, visit their website at sourcingbot.com and start finding parts!