Power Tips: What’s in a reference design?

I have a 10-month old daughter.  As many of you with children know, the sleeping schedule can be a bit tricky.  Sometimes I find myself up late at night getting drawn into infomercials.  I have seen so many I can pretty much predict what is going to happen.  My favorites include: “But wait! That’s not all!” and “If you call right now, we are going to double the offer!”  I never buy anything (unless I see it in the store months later), but the ideas are great and usually entertaining.

PowerLab notes have been around for 6 months and PowerLab itself for over a year, but I have not explained what exactly is included in a typical PowerLab design, or why. I thought I’d give it a go now, infomercial-style.  Maybe you will be enticed enough to give it a try, “it is free after all!”

Every design included in PowerLab started with a set of specifications from a real world application.  These specifications come from engineers looking for power solutions to fit in a system.  Once we have received the specifications, we start choosing the right TI parts for the job. 

From there, the first piece of collateral generated is the schematic.  The schematic is the first and most important piece developed because everything builds from this point.  Generally, we share the schematic with a customer and have some back and forth discussions to make sure all of the specifications are covered.  Changes are easily implemented at this time and become more difficult as time goes on. 

Example schematic from the PMP7390:

During the schematic design process, the choice of certain parts is very crucial.  It is important to make sure that parts that are chosen are the best for the job and readily available.  Parts can become obsolete or not recommended for new designs (NRND).  Once we narrow down all of the parts, a bill of materials (BOM) is generated.  The BOM is included with every PowerLab design.

Example BOM:

So now we have a schematic and BOM, next up is the printed circuit board (PCB) layout.  This step will create the artwork that is necessary to have physical boards generated.  The PCB layout is crucial to power supply design and can be the difference between the supply working and not working.  All PowerLab designs will include layout guidelines, photos of the PCB and many include the actual PCB design file and Gerber files (necessary to get the PCB built). All of the information to build the power supply has been included.

Example of board photo from the PMP7390:

“But wait there’s MORE!”

All reference designs in PowerLab are fully tested which means each includes a full test report including but not limited to the following:

  1. Power up waveforms
  2. Output voltage ripple
  3. Transient response (load step response)
  4. Efficiency
  5. Load Regulation
  6. Switching waveforms
  7. Thermal images

Examples of test data from the PMP7390:

I (or another design engineer) then captures and verifies all test data.  Fellow TI engineer, Bob Hanrahan, produced 4 Engineer It videos on how to test power supplies with specific focuses on measuring efficiency, measuring stability, and measuring noise. You can watch the overview below, or click one of the previous links for more specific testing.

How to test power supplies – overview

In summary, if you choose a PowerLab  reference design, this is what you are going to get:

  1. Schematic
  2. BOM
  3. PCB Layout
  4. Test Report

If you have any questions, ask away in the comment section below. If you have used a PowerLab reference design, tell me your experience. I would love to hear!

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