The DAC90802 implements a current-steering R-2R ladder architecture. Figure 6-1 shows a typical equivalent DAC channel. Each DAC contains a matching feedback resistor for use with the internal I-to-V conversion amplifier. The RFB pins are connected to the output of the amplifier.

The DAC90802 support both DC and AC reference voltage inputs. A matched internal feedback resistor network at RFB allows users to digitally select the gain G_FB of the DAC output voltage either as 1V/V, 2V/V or as 4V/V. Power along with the proper gain selection must be applied to the device to achieve continuity while measuring RFB. Equation 1 defines the DAC transfer function.

Where,

${\mathrm{G}}_{\mathrm{F}\mathrm{B}}=\frac{{\mathrm{R}}_{\mathrm{F}\mathrm{B}}}{{\mathrm{R}}_{\mathrm{D}\mathrm{A}\mathrm{C}}}$ is the gain setting of the DAC,

$\mathrm{n}$ is the programmed DAC code,

$\mathrm{N}$ is the DAC resolution,

${\mathrm{V}}_{\mathrm{R}\mathrm{E}\mathrm{F}\mathrm{P}},\mathrm{ }{\mathrm{V}}_{\mathrm{R}\mathrm{E}\mathrm{F}\mathrm{N}}$ are the reference voltages applied to VREFP and VREFN pins respectively,

${\mathrm{V}}_{\mathrm{O}\mathrm{F}\mathrm{F}},\mathrm{ }{\mathrm{V}}_{\mathrm{A}\mathrm{D}\mathrm{J}}$ are the coarse-offset and fine-offset voltages applied to using ROFS and VOSADJ pins, respectively (see Section 6.3.1.4 for details),

${\mathrm{G}}_{\mathrm{O}\mathrm{F}\mathrm{F}}=\frac{{\mathrm{R}}_{\mathrm{F}\mathrm{B}}}{{\mathrm{R}}_{\mathrm{O}\mathrm{F}\mathrm{S}}},\mathrm{ }{\mathrm{G}}_{\mathrm{A}\mathrm{D}\mathrm{J}}=\frac{{\mathrm{R}}_{\mathrm{F}\mathrm{B}}}{{\mathrm{R}}_{\mathrm{V}\mathrm{O}\mathrm{S}}}$ are the coarse-offset adjust and fine-offset adjust gains respectively (see Section 6.3.1.4 for details),

and,

${\mathrm{V}}_{\mathrm{O}\mathrm{U}\mathrm{T}}$ is the DAC output voltage

For basic unipolar operation (without offset or adjust voltages), where ${\mathrm{V}}_{\mathrm{R}\mathrm{E}\mathrm{F}\mathrm{P}}=0,\mathrm{ }{\mathrm{V}}_{\mathrm{R}\mathrm{E}\mathrm{F}\mathrm{N}}=\mathrm{ }-{\mathrm{V}}_{\mathrm{R}\mathrm{E}\mathrm{F}}$

and the zero-code, mid-code and full code values are

${\mathrm{V}}_{\mathrm{O}\mathrm{U}\mathrm{T}}^{\mathrm{n}=0}=\mathrm{ }0,\mathrm{ }{\mathrm{V}}_{\mathrm{O}\mathrm{U}\mathrm{T}}^{\mathrm{n}=2^{\mathrm{N}-1}}=\mathrm{G}\times \frac{{\mathrm{V}}_{\mathrm{R}\mathrm{E}\mathrm{F}}}{2},\mathrm{ }{\mathrm{V}}_{\mathrm{O}\mathrm{U}\mathrm{T}}^{\mathrm{n}=2^{\mathrm{N}}-1}=\mathrm{G}\times {\mathrm{V}}_{\mathrm{R}\mathrm{E}\mathrm{F}}(\mathrm{ }1-\frac{1}{2^{\mathrm{N}}})$ respectively.

For basic bipolar operation (without offset or adjust voltages), where ${\mathrm{V}}_{\mathrm{R}\mathrm{E}\mathrm{F}\mathrm{P}}=\mathrm{ }{\mathrm{V}}_{\mathrm{R}\mathrm{E}\mathrm{F}},\mathrm{ }{\mathrm{V}}_{\mathrm{R}\mathrm{E}\mathrm{F}\mathrm{N}}=\mathrm{ }-{\mathrm{V}}_{\mathrm{R}\mathrm{E}\mathrm{F}}$

and the zero-code, mid-code and full code values are

${\mathrm{V}}_{\mathrm{O}\mathrm{U}\mathrm{T}}^{\mathrm{n}=0}=\mathrm{ }-\mathrm{G}\times {\mathrm{V}}_{\mathrm{R}\mathrm{E}\mathrm{F}},\mathrm{ }{\mathrm{V}}_{\mathrm{O}\mathrm{U}\mathrm{T}}^{\mathrm{n}=2^{\mathrm{N}-1}}=0,\mathrm{ }{\mathrm{V}}_{\mathrm{O}\mathrm{U}\mathrm{T}}^{\mathrm{n}=2^{\mathrm{N}}-1}=\mathrm{G}\times {\mathrm{V}}_{\mathrm{R}\mathrm{E}\mathrm{F}}(\mathrm{ }1-\frac{1}{2^{\mathrm{N}-1}})$ respectively.