A typical output-voltage long-term stability characteristic is shown in Figure 2.įigure 2.Typical output-voltage long-term stability. An application's long-term stability can be improved by PCB-level burn-in. Cumulative drift beyond a 1000-hour interval is not generally specified, but is usually much lower than the initial drift. This is the change in reference output voltage vs. Where ΔV REF is the change in reference voltage caused by the temperature cycle. It is specified as a ratio of the two voltages and expressed in ppm: This is the change in reference voltage at +25☌ after the temperature is cyc led from T MIN to T MAX. Note that this is more important with some DAC topologies such as R-2R ladders, while resistive string topologies are less susceptible.
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This change is generally small, but should be considered in high-accuracy applications.
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Therefore, as the code changes, the reference input imp edance will also change, causing a change in reference voltage. Some DACs may not buffer the reference input. This term defines the incremental change in output voltage for a change in load current. This term defines the incremental change in output voltage for a change in input voltage.
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With series references, therefore, it is generally not possible to relate voltage drift and temperature so that one can calculate the drift over a specific range other than that over which the part is specified. Two different example curves are shown, both of which satisfy the 5ppm/☌ specification over -40☌ to +85☌.įigure 1. Note that some devices are specified over several temperature ranges.Ī graphical example of the box method is shown in Figure 1. If, however, one chose a reference specified over the -40☌ to +85☌ range, a reference that is 1050/125 = 8.4ppm/☌ or better would be required. This reference value works out to 1050ppm over the range. For instance, the MAX6025A is specified as a 15ppm/☌ reference over 0☌ to +70☌. It is generally best to select a device that is specified over the required temperature range, rather than a broader range. Thus to illustrate, if a part has a temperature coefficient of 5ppm/☌, specified from -40☌ to +85☌, the maximum de viation over temperature would be:
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So, to calculate the maximum change, multiply the temperature coefficient by the temperature range for the part. The limits of the output voltage do not necessarily coincide with the limits of temperature. temperature characteristic is not specified only the limits of this function are specified. This is the change in reference output voltage, measured for a given change in temperature and spec ified in ppm/☌. This is the output voltage tolerance, ignoring any effects of temperature, input voltage, and load. Voltage Reference Specifications Initial Accuracy
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Only those factors relevant to the error budget will be discussed here. Voltage references and DACs have many specifications. To design a system, one must first understand how the parts are specified and then how their performance characteristics interact. This applica tion note focuses on Maxim's 3-ter minal voltage references and precision DACs. The components' specifications can be traded off against each other to ensure that system specifications are met at the lowest cost. Consequently, selection of both DAC and reference should be made together. When designing a digital-to-analog converter (DAC) system, the DAC specifications and its voltage reference work in tandem to produce the overall system pe rformance. The calculations are av ailable in a spre adsheet. It describes the calculations required to select the data converter and the reference to meet the system’s target specifications. The analysis focuses on the factors introduced by both the data converter and the voltage reference. Calcula TIng the Error Budget in Precision Digital-to-Analog Conver ter ( DAC) Applica TIonsĪbstract: This applica TIon note analyses the pa ramete rs that affect the errors in precision digital-to-analog converter (DAC) applica TIons.