1

INTRODUCTION

When an adjustable shunt voltage reference like

TL431 is used in programmable mode, we may

encounter some errors due to the programmation.

This application note will give to the reader a

method to determine the relative error on the

output voltage.

The schematic used to program a shunt voltage

reference is presented on

reference provide some relative errors: this is

what we call the inner precision. As we have to

use an external resistor bridge configuration, we

obviously have some additional errors as all

resistor elements are not perfects.

The application note will present the calculation in

order to reach a final formula which can be used

easily to calculate the relative error of the global

schematic.

The following elements are taken into account:

Fig. 1: Typical application schematic of a shunt voltage reference

TL431

R2

R1

R

VCC

V

Vref

TL431

R

VCC

V

Vref

V = ( 1 + R1 / R2 ) x Vref + R1 x Iref

Iref

V = Vref

APPLICATION NOTE

AN1761

TL431

Accuracy of shunt voltage references in programmable mode

by Jérôme D’Agostino

Revision A

1/3

September 2003