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MMA8451QR1 drawing 20 mA?

Question asked by Kevin King on Apr 3, 2015
Latest reply on Apr 14, 2015 by Jacques Trichet

Hello everyone.  I have a design using the MMA8451QR1 accelerometer.  When the board is first powered up, it draws 15~20 mA.  After it is initialized the current drops back to the uA range as specified in the DS.  We have 5 prototypes built and they are all exhibiting the same behavior.  It should also be noted that the parts came from two different orders from DigiKey.

 

The part does work correctly and gives the expected responses to movement.  We haven't been able to dial in on exactly what line of code causes the power consumption to drop (the developer who wrote the software isn't available this week), but once we initialize the I2C and begin actually polling the FIFO of the part, we see current consumption drop.  We also see the part get warm on our thermal imager (that's how we discovered this is where our current was going in the first place), but once the I2C is initialized and we start polling the FIFO, the temperature rapidly drops back to ambient and the part becomes the same temp as the rest of the board.

 

I have attached a pic of the schematic as to how it is wired.  As required in the reference design, pin 3 ("DNC") is not connected and is floating. We did connect the "NC" pins to ground, though we removed the part from one board and cut those pads out (the "NC" pads, pins 8, 13, 15, 16) and re-installed the part and the behavior still persists.

 

We are ready to kick off production and we'd like to get a warm fuzzy feeling as to why this is happening and if it's safe to move ahead.

 

Any feedback much appreciated.  Thanks!!

-K

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