[FAQ] REF70: Voltage Reference Calibration

Hello,

There are some ways in which a voltage reference can be calibrated:

1. Initial Accuracy and Solder shift Calibration

Separating solder shift and initial accuracy on a soldered device is very difficult. Initial accuracy and solder shift are gain errors that can both be calibrated and this is common in very high resolution systems but not so often in low resolution systems due to calibration cost. Solder shift can be calibrated out the same way initial accuracy can be.

Single-point calibration can remove voltage reference DC errors. Start-up calibration and run-time calibration are single point calibration tests that are beneficial because these tests can remove the voltage reference DC errors that contribute to gain errors at the site of operation.

These gain errors are typically calibrated out by measuring the output voltage of the voltage reference at 25C to know the deviation. By knowing this value, the effect becomes negligible or non-existent as the value can be taken into account in the digital calculations.

2. Temperature Calibration

Temperature calibration is more effective in smaller temperature windows. Due to this designers must know the operating temperature the device experiences. The temperature drift varies slightly from voltage reference to voltage reference. Therefore, it can be difficult to calibrate out the error across multiple devices using the same profile. We recommend to calibrate each voltage reference with a unique profile. The drawback of multi-point calibration is the increase of cost, calibration time, and the fact that not all temperature curvatures are easy to calibrate. Choosing a more precise voltage reference which has better temperature drift, such as REF50, REF54, or REF70, to avoid performing multi-point calibration can be the best option. For lower power voltage references, devices like REF35, REF34, REF33, REF4132, and REF20 also provide good temperature drift.

For more information on calibration methods and error approximation, please see this application note: https://www.ti.com/lit/an/snaa320b/snaa320b.pdf

Thanks,

Jackson