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). Figure 1. Circuit shows current-to-voltage conversion. Compact Solution 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. We Want Your Feedback! Automatic Updates Would you like to be automatically notified when new application notes are published in your areas of interest? Sign up for EE-Mail™. More Information   APP 4075: Jul 20, 2007 DS1864 SFP Laser Controller and Diagnostic IC Full Data Sheet (PDF, 644kB) Free Samples MAX4233 High-Output-Drive, 10MHz, 10V/µs, Rail-to-Rail I/O Op Amps with Shutdown in SC70 Full Data Sheet (PDF, 1MB) Free Samples   Download, PDF Format (25kB)  AN4075, AN 4075, APP4075, Appnote4075, Appnote 4075