How to Use the DS1864's Current DACs as Voltage DACs

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.
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.

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.
Next Steps
EE-Mail Subscribe to EE-Mail and receive automatic notice of new documents in your areas of interest.
Download Download, PDF Format
© , Maxim Integrated Products, Inc.
The content on this webpage is protected by copyright laws of the United States and of foreign countries. For requests to copy this content, contact us.
APP 4075:
TUTORIALS 4075,AN4075, AN 4075, APP4075, Appnote4075, Appnote 4075