Long-Term Drift in Voltage References
Long-Term Drift in Voltage References
Multiple industrial applications, such as grid monitoring and remote field sensors, require instrumentation that operates with high precision over a long period of time. For such use cases with long life times, the Long-Term Drift (LTD) parameter of voltage references, becomes critically important. This application note describes the Long-Term Drift parameter, factors which affect it, how it is measured and gives sample profiles of some of the TI precision voltage references.
Trademarks
All trademarks are the property of their respective owners.
1 Long-Term Drift
The reference voltage is a critical component in a signal chain and can impact the performance if careful consideration not provided to various the error sources. The output of the voltage reference varies depending on the temperature, input voltage, load current, and time. This application note focuses on deviations of the output voltage over time due to aging known as Long-Term Drift (LTD) or long-term stability. LTD is a key parameter in industrial and automotive applications where a system will not experience regular calibration over its lifetime. The error from LTD can dominate all other errors over time. Therefore, it is important to understand how the parameter is tested and specified for the data sheet.
2 Long-Term Drift Data Sheet Measurement
Long term drift (LTD) for voltage references give insight of its output behavior over long period of time in a quantitative manner. Long-Term Drift Equation shows how Long-Term Drift is typically defined in a data sheet electrical characteristics table.
Where:
- VOUTt0 = Output voltage at the start of measurement. This is done right after soldering.
- VOUTtn = Output voltage at nth hour
During this measurement the reference was powered up for n hours.
The resulting value is then captured in the data sheet in Figure 2-1 based on the amount of time tested and measured. LTD is not production tested; therefore the value specified is a typical value that will have variation across devices. Examples of variations can be found in the typical characteristic graphs in the data sheet. This table shows two LTD values based on two time subdivisions from the same continuous test for the DBV package, the first 1000 hours and the subsequent 1000 hours for a total of 2000 hours.
Figure 2-1 Long-Term Drift Data Sheet Table
Example for REF34-Q1The LTD specification in the electrical characteristics table can be used for generic error calculations but the graphs in the data sheet show the actual trend over time. The graphs illustrate that the drift is not consistent in value or direction from unit to unit but generally the drift slows over time. The LTD primarily comes from the mechanical stress and aging, so as the packaging, bonding and die materials settle over time, the drift will slow down.
