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ADAU1372 I2C bus goes away when I apply oscillator to MCLKIN

Question asked by buzmeg on Jun 17, 2017
Latest reply on Jun 19, 2017 by buzmeg

I have the I2C working fine for the ADAU1372.  It responds with the appropriate values at the expected address (0x3D); I can read and write the initial registers and read them back.  I can read the default reset values just fine.

 

And then I enable my oscillator on the MCLKIN pin, and my I2C goes AWOL.  I can't get it back until I cause the PD pin to go low *AND* I disable the oscillator again.  If I leave an oscillating signal on MCLKIN, I can reset the part until the end of time and my I2C won't come back.  Once I disable the oscillator on the MCLKIN pin, then resetting the part gets my I2C back.

 

This feels like the part is switching to SPI mode somehow.  I'm a bit stumped, though, as I have Pin 4 (SS_/ADDR0) hardwired to Vdd to explicitly prevent this from happening.

 

Has anybody else seen this?  Is this something that would happen if a ground pin isn't soldered right?  I'm very confused.

 

Thanks for any help.

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