I have designed a board which contains four AD5422B DACs.Each DAC has been programmed to generate 4mA output.
Here are the four output currents measured. Output 1 = 3.999mA, Output 2 = 4.001mA, output 3 = 4.053mA, Output 4 = 3.999mA.
The load resistor for this test is 250Ohms.
I am trying to determine why output 3 is so high. The measured reference voltage is 4.9976 mV.
I programmed the part initially to use Rext and changed to Rint without any noticeable difference.
Because AVDD comes up after DVCC in this design, a reset command is issued to all DACS first. Sheet 29 recommends a settling time of 40usec but I increased it to 100 useconds but again didn't notice any difference in output.
The boost transistor is recommended in the data sheet.
Attached is a page from the schematic showing two of the AD5422B circuits.
I would appreciate any ideas.