9.2.1 Design Requirements

This design requires two channels of the DACx0004 to generate a bipolar output. The design is very flexible and allows for many different configurations. Typically, one channel is used to finely control the output, while the other is used to offset the output. The direction of the offset depends on which channel is used as an offset. DAC_POS provides a positive offset and DAC_NEG has a negative offset.

9.2.2 Detailed Design Procedure

The output of each DAC can be modified via the digital interface and the gain of each output can be modified independently by changing the external resistors. In order for the gain of each offset to be independent, Equation 2 must be true.

Equation 2.

The output voltage range, V_OUT, is adjusted according to Equation 3. Keep in mind that Equation 3 is only true when Equation 2 is true.

Equation 3.

Each DAC outputs a voltage from 0 to REFIN. As an example, if DAC_POS gain is 1, DAC_NEG gain is 2 and R_FB = 2 kΩ, then R_POS = 2 kΩ, R_NEG = 1 kΩ and R_A = 1 kΩ. With the correct digital implementation it gives the output an effective output range of ±15 V, with discrete 16-bit steps.

9.2.3 Application Curve

Figure 59 displays two different modes of operation. Mode 1 gains the output of DAC_Neg by a factor of 2 and maintains DAC_POS at unity gain. Mode 2 reverses the gains of each stage to invert the system. These are just two examples of the types of outputs that can be achieved using this configuration.

Figure 59. Output Voltage vs Fine DAC Input Code