Keywords: DS1864, current DAC, voltage DAC, current to voltage Related Parts
APPLICATION NOTE 4075
How to Use the DS1864's Current DACs as Voltage DACs
Jul 20, 2007
Abstract: This article describes how to convert the current DACs in the DS1864 SFP laser controller/monitor to a voltage output by using standard components.
The Current DACs
The DS1864 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.
Current-to-Voltage Conversion
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).
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.
UCSP is a trademark of Maxim Integrated Products, Inc.
