SNAA320B November   2019  – January 2024 LM4040-N , LM4050-N , LM4128 , LM4128-Q1 , LM4132 , LM4132-Q1 , REF102 , REF1925 , REF1930 , REF1933 , REF1941 , REF20-Q1 , REF200 , REF2025 , REF2030 , REF2033 , REF2041 , REF2125 , REF2912 , REF2920 , REF2925 , REF2930 , REF2933 , REF2940 , REF3012 , REF3020 , REF3025 , REF3030 , REF3033 , REF3033-Q1 , REF31-Q1 , REF3112 , REF3120 , REF3125 , REF3130 , REF3133 , REF3140 , REF3212 , REF3212-EP , REF3220 , REF3220-EP , REF3225 , REF3225-EP , REF3230 , REF3230-EP , REF3233 , REF3240 , REF3312 , REF3318 , REF3320 , REF3325 , REF3330 , REF3333 , REF34-Q1 , REF3425 , REF3425-EP , REF3430 , REF3430-EP , REF3433 , REF3433-EP , REF3440 , REF3440-EP , REF3450 , REF35 , REF4132 , REF4132-Q1 , REF5010 , REF5020 , REF5020-EP , REF5020A-Q1 , REF5025 , REF5025-EP , REF5025-HT , REF5025A-Q1 , REF5030 , REF5030A-Q1 , REF5040 , REF5040-EP , REF5040A-Q1 , REF5045 , REF5045A-Q1 , REF5050 , REF5050-EP , REF5050A-Q1 , REF54 , REF6125 , REF6133 , REF6141 , REF6145 , REF6150 , REF6225 , REF6230 , REF6233 , REF6241 , REF6245 , REF6250 , REF70 , TL431LI , TL432LI , TLV431

 

  1.   1
  2.   Abstract
  3.   Trademarks
  4. 1 Introduction
  5. 2 Analog-to-Digital Converter Error
  6. 3 Voltage Reference DC Error
    1. 3.1 Initial Accuracy and Solder Shift
    2. 3.2 Temperature Drift
    3. 3.3 Line Regulation
  7. 4 DC Error Calculations
  8. 5 Calibration
  9. 6 Voltage Reference Noise Error
    1. 6.1 1/f Noise
    2. 6.2 Broadband Noise
    3. 6.3 Power Supply Rejection Ratio
    4. 6.4 Noise Example
  10. 7 Dynamic Error (Voltage Reference Driving Capability)
  11. 8 Low Power Applications
  12. 9 References
  13. 10Revision History

3.1 Initial Accuracy and Solder Shift

Initial accuracy of a system dictates how close a reference voltage is to the nominal voltage at 25C. This voltage deviation typically has a max deviation that is given in percent. Typical values of initial accuracy are 0.05% to 2% (500 – 20,000ppm). This wide range of initial accuracy values can be used to separate reference voltages into different tiers of accuracy such as in Table 3-1. Initial accuracy is also only valid for the specified conditions on the electrical characteristics table.

Table 3-1 Initial Accuracy
ACCURACY RANGE
High < 0.1%
Medium 0.1% - 0.5%
Low > 0.5%

One common misconception is that the reference voltage error measured on a soldered PCB board at 25C is just a component of initial accuracy. This statement is incorrect because every device that is soldered experiences an initial thermal shock that can affect the initial accuracy of the device. The deviation due to solder shift is not always reported on a data sheet but even if the solder shift is not reported, this is a physical phenomena that is always present. If a design requires a device to go through multiple solder reflows then the expected deviation is much larger. Separating solder shift and initial accuracy on a soldered device is very difficult. Note that the initial accuracy and solder shift do not include the effects of accuracy shifts from long term shift, thermal hysteresis, or thermal drift.

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. In low resolution systems, consider that the initial accuracy and solder shift can be the largest DC errors a voltage reference. If there is no calibration in the system then the initial accuracy is a dominant factor and is important to choose the device with the best accuracy to lower the total error. In higher resolution systems the initial accuracy and solder shift must be calibrated out as even a 0.1% difference in accuracy across devices can severely degrade the performance of 18-bit resolution systems. Therefore 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.