Wednesday, March 23, 2011

STMicro's STMPE16M31 - A classic example of cumbersome power supply and signal level design.

STMicro's STMPE16M31 is a touch sensor IC that is designed to operate from one external power supply between 2.7 and 5.5V.  Great, right?  Well the dirty little secret on this thing is that its interface signals are scaled at 1.8V. 

Why not buffer these signals internally to match the input supply voltage of 2.7 to 5.5V?  That would make a lot more sense to me, considering I have this supply voltage available, which means I probably use it as a signal level.  Instead, they assume I have 1.8V signaling capabilities available.  If I had that, then I would probably have a 1.8V voltage supply I could power the device from - and it would be significantly more efficient than their internal regulator.  Also, the rail inside the IC is probably at a different voltage than the 1.8V level I use outside the device, which means my signal level will be slightly different as well - probably not an issue looking at the spec sheet, but it doesn't make me feel any better about the design.

The part seems to work great, but I hate the complexity of making a design around it.

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