Deeply embedded design


Posted on Feb 4, 2014

The following is an account of such an undertaking. Recently I was involved in a design review for a cost reduction project, where an older design was getting an update. The new design was a merging of two different designs, including someupdated parts and some existing controls. The design includes six 10Amp H-bridge drivers and the associated control logic. Some of the early testing had shown


Deeply embedded design
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some rather large current spikes and also some higher than desirable amounts of electromagnetic interference (EMI). A consultant who had been helping out on a similar design, mostly on EMI concerns, had suggested a few timing changes to the circuitry. As the talks continued, two different schemes involving changes to the timing were discussed. At this point, I had jumped in and suggested that we pull out all the control circuitry and replace it with a small microprocessor or a CPLD, allowing us some freedom to make changes in the timing schemes. My manager had referred to my suggestion as "a small joke", but I assured him I was serious. A couple of days later I met with my manager and we talked a little more about the idea of handling the bridge control logic inside of a small microprocessor. After we are able to agree that it would in fact be possible (and also a good idea to do so), we quickly defined the desired level of control and the range of the different delays that we would need to consider. Great, we have a plan and a direction. Before we jump into the work, let`s take a moment and analyze the current circuit to determine present functionality and the actual delay times in order to better understand our starting point. The big picture view on the circuit is actually quite simple. Changes in the `Direction` line require proper sequencing of the current source and the bridge drivers. On a change in direction, the...




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