# Linearity of a DAC0800 Current Output R2R DAC

The DAC0800 is a current output R-2R DAC with 8 bits of resolution. As part of a solar panel monitor, the DAC0800 serves as a programmable reference for a shunt regulator. The output of the DAC is mirror 1:1 into a $$5\;k\Omega$$ load; forming the voltage reference for the shunt regulator. A simplified schematic of the DAC is shown below.

The DAC is swept from code 0 to code 255 and the output of the shunt regulator is recorded. The resulting transfer function of programmable shunt regulator is shown in the figure below.

The integral non-linearity of the system is determined as the residual form a least-squares fit of a first order function. The plot below depicts the system INL, the magnitude is normalized to LSBs.

A worst case INL of 0.24 LSB is observed at the full-scale code (255).

DNL of the system is measured as the difference from 1LSB at each code step.

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