LINEAR AN82-1 Data Handbook/Specifications Sheet

Application Note 82

November 1999

Understanding and Applying Voltage References By Mitchell Lee

Specifying the right reference and applying it correctly is a more difficult task than one might first surmise, consid- ering that references are only 2- or 3-terminal devices. Although the word “accuracy” is most often spoken in

reference to references, it is dangerous to use this word

too freely because it can mean different things to different people. Even more perplexing is the fact that a reference

classified as a dog in one application is a panacea in another. This application note will familiarize the reader with the various aspects of reference “accuracy” and

present some tips on extracting maximum performance from any reference.

HP MIRRORED

SCALE CO UN TS

As with other specialized electronic fields, the field of

monolithic references has its own vocabulary. We’ve

already learned the first word in our reference vocabulary, 0.3 3,000

“accuracy.” This is the yardstick with which references are BI TS graded and compared. Unfortunately, there are at least five

–60 0.1 –3 1,000 PE RC EN

or six good units for gauging accuracy. To keep you from

reaching a full understanding of the topic, industry pundits

–70 0.03 PO ER OF EN

use a special technique called “unit-hopping” to confuse

and confound everyone from newcomer to seasoned PP

veteran. You mention an accuracy figure and the pundit

quickly hops to a new unit so that you cannot follow his line

of reasoning. Figure 1 neutralizes the pundits’ callous

32,768 –90 0.003 DV IG IT

intentions and allows its possessor to unit-hop with equal

ease and full comprehension. Refer to Figure 1 as you read

this application note.

Today’s IC reference technology is divided along two 1–2

lines: bandgap references, which balance the tempera- 262,144

ture coefficient of a forward-biased diode junction against

that of a ∆VBE (see Appendix B); and buried Zeners (see

Appendix A), which use subsurface breakdown to achieve 1,048,576

outstanding long-term stability and low noise. With few 1–2

exceptions, both reference types use additional on-chip

circuitry to further minimize temperature drift and trim 4,194,304

output voltage to an exact value. Bandgap references are

generally used in systems of up to 12 bits; buried Zeners

16,777,216 AN82 F01

take over from there in higher accuracy systems. , LTC and LT are registered trademarks of Linear Technology Corporation. Figure 1. Accuracy Translator

AN82-1