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AD5504 works, unless I have more than 1

Question asked by MTJones on Jan 17, 2014
Latest reply on Jan 23, 2014 by KenK

I am communicating with an AD5504 with a microcontroller through USB.  I can power up the DACs and write to the individual input registers.  Everything works as it should, until I have two or more AD5504 chips in the circuit. 


In my current circuit I only have two AD5504 chips, a microcontroller and an FTDI USB to serial UART interface IC in between the microcontroller and USB.  In the end I will have 4 AD5504's as well as some other components in the circuit.  If I remove one of the AD5504's everything works just fine; however, with both in the circuit, control register writes typically fail.  Sometimes one or both AD5504s will respond to control register writes, but typically neither or on occasion one will respond to input register writes.  Without any changes to hardware or software, the control and input register responiveness that I get changes each time I provide power.  Again, however, if there is only one AD5504 in the circuit then the response does not very and it works correctly every time. 


There should be plenty of power/current available from the USB (~100mA).  I have connected the circuit to a power supply (several amps available) and removed the USB, so I don't think lack of power or current is an issue. 


I have not tried reading the MISO lines, but I am not sure what I would look for if I did.