Dear Sir, we made the circuit attached using the AD5421.
The loop power is 24V and I use for testing a 120ohm resistor.
Setting of the device is done for 4 to 20mA.
SPI is decoupled using the ADUM 3151 with a clock of 78KHz.
Everything is working, the precision of the current is excellent but the problem is that it is not possible to go below 5mA.
I tried also to power the ADUM5131 using a separated L78L33 leaving unconnected REGOUT with the result the minimum current grown up to 8mA.
I kindly ask a support.
Thanks and best regards.PDF