Ka-Boom: Power Management Circuitry, Where Not to Skimp on Design

In this modern, über cost conscious age, where every organization is trying to lean up or cut corners, depending on one’s perspective, there are a few places where it’s just plain dumb to cut corners (see also It’s Not All About Costs).  One of those is safety.  But safety issue are not limited to medical instruments or heavy machinery or toxic gases.  One of the most potentially dangerous objects in most homes and work environment is the ubiquitous lithium battery.  They’re in toys, phones, laptops and yes, electric vehicles.  And they can catch fire and blow up if not properly handled, as exhibited by recent highly publicized instances  of iPhone  and Chevy Volt fires.

But here’s the rub: they absolutely will catch fire or even worse explode if the circuitry surrounding the batteries is not implemented extremely well.  Not can, will.  And furthermore, with products containing such batteries becoming more and more common place, many design teams and especially non technical management are starting to think the the design and test of the power management circuits that surround these batteries is simple.  It is not.

The technical issues are complex and completely unsuitable for solving via a blog.   But we see far too many teams hoping to bang out a “simple” design ignore the complexities of this. Just pick up a reference design  and ka-ching, a working design ready to sell.  Or KA-BOOM. Possibly literally.

The devil is in the details, designing  the power management circuitry carefully, considering both hardware and software.  If the software freezes while charging, or if, as was reportedly the case in one of the iPhone instances, heavily utilized, the charging circuitry still needs to function properly.  Related to this is the imperative of  identifying all possible fault conditions and failure modes via an Failure Mode Effects Analysis, or FMEA (see FMEA: the Most Important Acronym that No One Knows) and in developing and executing a proper design validation test, or DVT, plan (see also Common Misconceptions about Design Validation Testing). Test these circuits in the lab–smoke in the lab beats smoke on an airplane any day (see also (promise this is the last) The Smoke Test)

One more sobering thought, and then I’ll get off this soap box:  both the iPhone and the Volt were designed and tested by some of the best engineering teams on the planet with massive budgets and superb labs.  These are world class products designed by world class teams who most likely cut far, far fewer corners than 99.9% of the product development teams out there, and they still have problems. Do not treat power management design and testing lightly. There are engineers who know how to do this, at Zebulon Solutions or at many other product development companies, as well as in many OEM labs.  Listen to these engineers. Please, before someone gets hurt.

Chuck

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