What would be the effect of the absolute accuracy and temperature drift of my external current setting resistor be to the accuracy of my AD5420's current output?
The % error of the External current setting resistor relates direct the gain error at the current output. It thus also will affect the TUE and full-scale error specifications. For example a 0.1% resistor with a worst-case drift specification of 5ppm/°C will contribute an additional error of 0.1%FSR and 5ppm/°C to the TUE/Gain error specification for external Rset.
So for the above 0.05%, 2ppm/°C resistor used with the AD5420, with a temperature range of -40°C to 85°C, the worst case TUE/gain error will be:
AD5420 with external Rset in %+ Absolute resistor error in %+ Resistor temperature drift in % * Temperature range
= 0.15%FSR + 0.05% + (0.0002% * 125°C)
So with this configuration the absolute worst case TUE/gain error due to the DAC and external Rset will be ±0.225%FSR. This could be compared to the specification with the internal Rset which achieved a 0.3%FSR specification.
Note that these calcualtions do not include the effect of the Reference variation.
Retrieving data ...