7.3.2 Reference Inputs

The reference high input, V_REFH, can be set to any voltage in the range of 1.25 V to AV_DD. The reference low input, V_REFL, can be set to any voltage in the range of –0.2 V to +0.2 V (to provide a small offset to the output of the DAC8881, if desired). The current into V_REFH and out of V_REFL depends on the DAC code, and can vary from approximately 0.5mA to 1mA in the gain = 1X mode of operation. The reference high and low inputs appear as varying loads to the external reference circuit. If the external references can source or sink the required current, and if low impedance connections are made to the V_REFH and V_REFL pins, external reference buffers are not required. Figure 67 shows a simple configuration of the DAC8881 using external references without force/sense reference buffers.

Kelvin sense connections for the reference high and low are included on the DAC8881. When properly used with external reference buffer op amps, these reference Kelvin sense pins ensure that the driven reference high and low voltages remain stable versus varying reference load currents. Figure 69 shows an example of a reference force/sense configuration of the DAC8881 operating from a single analog supply voltage. Both the V_REFL and V_REFH reference voltages are set to levels of 100 mV from the DAC8881 supply rails, and are derived from a 5-V external reference. Figure 71 and Figure 70 illustrate the effect of not using the reference force/sense buffers to drive the DAC8881 V_REFL and V_REFH pins. A slight degradation in INL and DNL performance of approximately 0.1 LSB may be seen without the use of the force/sense buffer configuration.

Figure 69. Buffered References (V_REFH = +4.900 V and V_REFL = 100 mV)

Figure 70. Linearity and Differential Linearity Error
for Figure 67 without Reference Buffers

Figure 71. Linearity and Differential Linearity Error
for Figure 69 with Reference Buffers