Analog Angle Blog

Meeting the ‘Rugged Design’ Challenge

Ruggedized products and extreme design are always of interest, since they pose an extra challenge to the designer. While I have no personal need for them, I am interested in them from an engineering perspective. That's why announcements that say “rugged” or similar get my attention. (You can search for “extreme design” in the search box in the upper right corner to see the some other case-study stories published on the Planet Analog site.)

For example, I just saw the TPS50601 and TPS50301 point of load (PoL) converters from Texas Instruments, which offer extra-range temp operation to +125&deg:C and +210&deg:C, respectively. These could certainly be the building blocks of a larger design, which needs to work despite that high-end temperature challenge. But if you step back and look at the bigger design picture, rugged components alone may not be enough to meet specs, yet ironically they may actually be too much.

Why the contradiction? It's because there are really two dimensions to the challenge of a rugged design. First, defining specifically what sort of “ruggedness” is needed: temperature, vibration, pressure (high and low), supply voltage, or ESD (electro-static discharge), to cite a few. It's obviously much more difficult to design for several of these factors, compared to just one.

Second is what strategy you should use to actually achieve the system-level goals. The quick and easy answer is to start at the bottom with rugged components (such as ICs that can stand the heat or ESD) and then work up to improving the larger parts of the design, such as the PC board assembly. Using suitable building blocks certainly seems like a good way to have a solid foundation for the ruggedization of the larger design.

However, that may not be the best approach in the overall system-level context. Perhaps it would be better to use standard components coupled with aggressive cooling, or an ESD-wise PC board layout with an array of discrete protection devices, for the situations above. As in all things related to a “best” design, there are tradeoffs and constraints.

Even if you have components that can tolerate the extremes (such as heat or ESD) without failure, there's the associated issue of system performance to spec. For example, do you select analog parts with very low and specified drift over the temperature range? Or do you choose to instead just “deal with it” by calibrating the system at various temperature points, and then using these calibration factors to correct the acquired data values? Do you do this calibration at the factory, or do you use a precision, wide-range voltage reference and calibrate the unit in the field, while it is operating?

Sometimes, choosing the in-use calibrate/compensate approach with easier-to-get, lower-cost components gives better overall performance than trying to meet electrical specs with an inherently stable design—however inelegant or brute force that method may seem.

On the mechanical side, designers face the same choices: using rugged components and then building up, or using standard parts and then ruggedizing at the system level, if possible (but it often isn't for mechanical design; you can't calibrate a support bracket to have better performance).

Have you ever had to do a rugged design? In which aspects was it ruggedized, and to what extent? What was the biggest challenge you had, and the biggest surprise you encountered?

11 comments on “Meeting the ‘Rugged Design’ Challenge

    March 14, 2013

    In the late 1990's I was asked to assist in designing down-hole power supplies. Down-hole is defined in the drilling industry as down in the earth where temperatures can reach the 150C-plus. The challenge here was to keep power dissipation to a minimum in order to keep the silicone chip temperature below 200C. 200C was there since above that value the device characteristics can change dramatically. A careful look at that temperature was primarily based on the temperatures that are needed to create the silicon chip as well; this can be as low as 250C. Thus having a 50C buffer before dramatic changes in the IC were important.

  2. eafpres
    March 14, 2013

    At one time many years ago I worked in a company that made analytical instruments.  These were boxes full of electronics, electromechanical parts, fluid handling, etc.  Becuase these were made for laboratory use, they were not required to be particularly rugged–they sat on a bench in a hosptiable environment for the most part.  We had the opportunity to fly one instrument on a Shuttle mission.  Surprisingly, the main issue we had to deal with was the electronics.  To achieve flight approval, we had to conformally coat all the boards.  This turned out to be quite simple, and a great solution if you have electronics that need to work in somewhat harsh environments–for instance, high humidity, possibilty of spills, etc.

    I think a lot of designs can be adapted using steps like conformal coating, additional cooling, better enclosures etc. instead of a bottom-up redesign.  As an example, this is going on a lot in the military use of off-the-shelf parts (so called COTS); vendors take standard electronics and repackage them in hardened enclosures or add active cooling and they can fly them on aircraft etc.

  3. Bill_Jaffa
    March 14, 2013

    Those who don't know, or worse, don't know and think they do, often simplistically assume you have to start with rugged components and build up to have a rugged overall system. But often that's not possible, due to availablity, cost, or time–so you have to build a rugged system from the top down rather than the bottom up.

  4. Netcrawl
    March 17, 2013

    Rugged design and extreme designs are military's top choice because they're packed with extra power and features, they capable of doing or excedding the average tools an do. I'm interested to them because its defies engineering, pushing the boundary of limits. thy you see those NSA-certified smartphones, they're cool, powerful and with extreme designs.

  5. Brad Albing
    March 19, 2013

    Those high-temp parts are pretty specialized. At my previous company, we had some in the portfolio – op-amps, V-regulators, and interface. They saw usage as you've mentioned – oil-well drilling to report status of the cutter head. Often treated as a disposable part. When the bit gets dull and gets pulled out and changed out for a sharp one, they toss the electronics and put a new one in place. So it's nice business if you can get it.

  6. Brad Albing
    March 19, 2013

    Part of the rugged designs that I find interesting are the rad-hard parts. Not so much just the parts, but the mechanism by which radiation messes with the parts – and then the design tricks that the IC design engineers do to work around the siuations that in lesser ICs would mean failure. Someone should write a book.

  7. RedDerek
    March 19, 2013

    One of the tricks for rad-hard design is to use ICs with large feature size such as 4-micron. The smaller features such as the newer ICs and processors are more susceptible to radiation. Sort of like a rad-hard part would be like a .22 bullet being the radiation hitting the 4-micron tank – not much effect. However, if the radiation is a 150mm round hitting the 25nm-feature tank – yes, there could be some major damage.

  8. Jim Stockton
    March 20, 2013

    The temperatures encountered in the downhole environment can be extreme. In the 70's Harris had op-amps tested to >300C. Most of their DI parts played well to >230C. Semiconductor vendors are just now re-discovering the high temperature market. At these temperatures component lifetimes are pretty short. The real challenge is to find parts that haven't been made useless by having thermal shutdown.

  9. Brad Albing
    March 23, 2013

    The Harris parts became part of the Intersil portfolio. Still some of the old ones available and occassionally a new one introduced.

  10. Brad Albing
    March 27, 2013

    How does one go about getting one of those NSA-certified smartphones? Seems like it might come with strings (or possibly Dick Cheney) attached.

  11. Brad Albing
    March 27, 2013

    I believe one of the rad-hard guys I used to work with was explaining something along those lines to me. I think I may still know where to find the White Papers the pertain to the design.

Leave a Reply

This site uses Akismet to reduce spam. Learn how your comment data is processed.