AnsweredAssumed Answered

AD5696 i2c issues

Question asked by PFFrockU on Apr 2, 2015
Latest reply on Apr 2, 2015 by PFFrockU

Hello,
   I have 3 of the AD5696 on a board and I'm trying to communicate via i2c (100khz) to update the outputs. Each of them have a different address (see sch below). The addresses are 0b0001100, 0b0001110 0b0001110 (0x0C, 0x0D, 0x0E).

I looked at the SLC/SDA lines under an Oscope and saw that while the address and the r/w bit were all correct, I'm still getting NACK from any chip. I even did a general scan of all i2c addresses, only to end up with no reply at all. I'm using an Ard Mega 2560 (ATmega16U2), to communicate with the chips. The DAC's seem to be properly soldered to the board, and I'm pretty much out of ideas. I set RSTSEL to high to verify that the DAC's give me midscale, and that worked no problem, so I don't believe that the chips are dead.



I read on the spec sheet that each chip has a max bus cap of 400pF, but the max bus cap on an i2c line is also 400pF, seeing as I have 3, I suppose I have a possible max of 1200pF, could that be a potential issue? Also, I have 10k pulls ups on the board as well as the 10k pullups on the mega, could that be making the pullups too low? Should I remove the pullups on the board?  Could either of those be the issue? Is there any method for me to find the problem?

 

Any help would be greatly appreciated.  

vRef =3.3v (from an on board regulator)

 

DAC layout.PNG

Outcomes