The Current DACs
contains two 8-bit current-sink DACs with 1.5mA or 0.5mA selectable full-scale range. The DAC outputs must be at a voltage level between 0.7V and the DS1864's VCC
An operational amplifier in differential amplifier configuration is used to convert the 0.5mA full-scale current-mode output to 1V full-scale voltage-mode output (Figure 1
Figure 1. Circuit shows current-to-voltage conversion.
Using a chip-scale packaged op amp and 0201 resistors will provide the most compact solution. The MAX4233
is a two-channel op amp available in 1.5mm x 2mm 10-bump UCSP™.
Output Voltage Calculation
The output voltage is calculated in Equation 1.
Using the values shown in the Figure 1 drawing, the maximum output voltage is 1.005V when the DAC current is 0.5mA. To minimize offset and gain errors, 1% tolerance resistors should be used. Further, R1 should be selected so that the voltage at the DAC pin never falls below 0.7V.