Discrete component designs save the day when proprietary ICs are in short supply

by Kevin Parmenter, Director, Applications Engineering North America, Taiwan Semiconductor

We have just exited a time of constrained supply vs demand, the scale of which has never been seen before, even in our cyclical electronic component business. Although we are used to cyclical downturns in our industry, the shortages this time were unprecedented. The causes are many when this happens in the supply chain — the pandemic, the Russian invasion, too much demand vs. too little capacity, wafer shortages, global instability, weather events, and so on. The difference with this recent downturn is that it has affected design engineers’ behavior and even major customers’ supply chain teams. If you are in a meeting, the supply chain teams can’t talk about anything other than “supply chain resiliency.” On the other hand, engineers are rethinking proprietary parts when they can avoid them.

For years, we have been taught that implementing a minimum-parts-count solution using highly dependable ICs is the best design approach. Are colleges even teaching discrete design anymore? As a design engineer, you would typically use ICs for functions like ramp generators, differential amplifiers, oscillators, switches, or gate drivers. But if your amazing proprietary IC takes 99+ weeks to obtain, you might regret that decision. You can likely use discrete devices — with backup sources for your less sophisticated circuit functions. That way, if one supplier decides to stop making, say, MMBT3604s, 1N4148s, or MMBT3906s, plenty of other suppliers are left to choose from, and you can keep going. Additionally, should you want something specific in your design, you are free to implement it using discrete components. Meanwhile, with ICs, typically, some functionality decisions have been made for you, and you cannot change them.

Sure, proprietary ICs meet the parts count and cost criteria, but perhaps new designs could contain dual layouts to hedge against production-limiting shortages. In this case, only one layout on the PCB is populated, and the other is not. If a part becomes unavailable, you can simply populate the alternate layout. This approach is, of course, more expensive — but it’s cheaper than not shipping products for two years.

Component suppliers must figure out a way to make their supply chains more robust, and it seems as if the customers are going to force this issue with supply chain meetings, surveys, and scorecards. It will get fixed, but it takes time. Fab facilities are expensive and take time to build. And I always add this: ” If forecasting actually worked as it should, this would never happen.” Right? But that’s the subject of another article.

Another challenge is that many suppliers are not committed to customer orders. When your backlog goes away after waiting out your initial 22-week lead time, only to see it suddenly turns into 99 weeks, it means that the supplier sold your parts to a more favored customer. (Nice, just wait some more.)  But your customers won’t remember, right?

Imagine a proprietary IC integral to your design is suddenly and randomly “EOL” ed.
I call it – “getting semiconductored.”

Figure 1 is an actual example of this problem. It shows a relay driver for an HVAC  75mA contactor. This single part offered many types of protection with one insertion in production; no external parts were needed, but it suddenly went EOL.

Solution: using discretes

What do you do now? Maybe change the design using what you should have used in the first place: discretes. How about a 2N7002? Lots of people make those. And we can add some 1N4148s or 1N4004s and TVS devices for protection using “common household materials” – the tried-and-true discrete parts we know so well.

Figure 2 shows the discrete design. “Q1” is a 2N7002. “D1” and the back EMF diode of the relay coil can be a 1N4148 or 1N4004, and “D2” can be a BZT52B9V1-G or a P4SMA9.1 or similar. “R1” can be approx. 100K ohms; however, it’s not critical – “R2” can be 100 ohms depending on the logic switching signal applied to the input of “R2,” it’s just there to protect the gate of the 2N7002.

And now you have a future-proof design that is built to last. None of the components are critical. Simply build the circuit, times two, and you have a replacement for the sole-source part. Are there any downsides to this design? I can’t think of any that matters.

Using this solution, you can keep going without risking costly production delays. Plenty of companies make these discrete devices. And all of us are good at making them in massive volumes. So next time you are working on a design, consider discretes and protect yourself from being “semiconductored.”

 

 

About the author

Kevin Parmenter is an IEEE Senior Member and has over 20 years of experience in the electronics and semiconductor industry. Kevin is currently director of Field Applications Engineering North America for Taiwan Semiconductor. Previously he was vice president of applications engineering in the U.S.A. for Excelsys, an Advanced Energy company; director of Advanced Technical Marketing for Digital Power Products at Exar; and led global product applications engineering and new product definition for Freescale Semiconductors AMPD – Analog, Mixed Signal and Power Division. Prior to that, Kevin worked for Fairchild Semiconductor in the Americas as senior director of field applications engineering and held various technical and management positions with increasing responsibility at ON Semiconductor and in the Motorola Semiconductor Products Sector. Kevin also led an applications engineering team for the start-up Primarion.

Kevin serves on the board of directors of the PSMA (Power Sources Manufacturers Association) and was the general chair of APEC 2009 (the IEEE Applied Power Electronics Conference.) Kevin has also had design engineering experience in the medical electronics and military electronics fields. He holds a BSEE and BS in Business Administration, is a member of the IEEE, and holds an Amateur Extra class FCC license (call sign KG5Q) as well as an FCC Commercial Radiotelephone License.