ADR520/ADR525/ADR530/ADR540/ADR550

Rev. A | Page 11 of 16

THEORY OF OPERATION

The ADR520/ADR525/ADR530/ADR540/ADR550 use the

band gap concept to produce a stable, low temperature

coefficient voltage reference suitable for high accuracy data

acquisition components and systems. The devices use the

physical nature of a silicon transistor base-emitter voltage in the

forward-biased operating region. All such transistors have

approximately a –2 mV/°C temperature coefficient (TC),

making them unsuitable for direct use as a low temperature

coefficient reference. Extrapolation of the temperature

characteristic of any one of these devices to absolute zero (with

the collector current proportional to the absolute temperature),

silicon band gap voltage. Thus, if a voltage develops with an

temperature coefficient reference results. The ADR5xx circuit

shown in Figure 18 provides such a compensating voltage (V1)

by driving two transistors at different current densities and

provides a stable voltage reference over temperature.

+

–

BE

+

–

V1

V–

V+

+

–

Figure 18. Circuit Schematic

APPLICATIONS

The ADR520/ADR525/ADR530/ADR540/ADR550 are a series

of precision shunt voltage references. They are designed to

operate without an external capacitor between the positive and

negative terminals. If a bypass capacitor is used to filter the

supply, the references remains stable.

All shunt voltage references require an external bias resistor

following considerations:

•

current to the ADR5xx, even when the supply voltage is at

its minimum value and the load current is at its maximum

value.

•

10 mA when the supply voltage is at its maximum value

and the load current is at its minimum value.

IN

L

OUT

CC

BIAS

I

I

V

V

R

−

−

=

(3)

ADR550

Figure 19. Shunt Reference

Precision Negative Voltage Reference

The ADR5xx is suitable for applications where a precise

negative voltage is desired. Figure 20 shows the ADR5xx

configured to provide a negative output.

–2.5V

ADR525

Figure 20. Negative Precision Reference Configuration

Output Voltage Trim

The ADR5xx TRIM terminal can be used to adjust the output

voltage over a range of ±0.5%. This allows systems designers to

trim system errors by setting the reference to a voltage other

than the preset output voltage. An external mechanical or elec-

trical potentiometer can be used for this adjustment. Figure 21

illustrates how the output voltage can be trimmed by using the

AD5273, an Analog Devices 10 kΩ potentiometer.

R1

470k

Ω

POTENTIOMETER

10k

Ω

ADR530

AD5273

Figure 21. Output Voltage Trim