AD586

Rev. G | Page 7 of 16

THEORY OF OPERATION

The AD586 consists of a proprietary buried Zener diode refer-

ence, an amplifier to buffer the output, and several high stability

thin-film resistors, as shown in the block diagram in Figure 5.

This design results in a high precision monolithic 5 V output

reference with initial offset of 2.0 mV or less. The temperature

compensation circuitry provides the device with a temperature

coefficient of under 2 ppm/°C.

Using the bias compensation resistor between the Zener output

and the noninverting input to the amplifier, a capacitor can be

added at the noise reduction pin (Pin 8) to form a low-pass

filter and reduce the noise contribution of the Zener to the

circuit.

A1

AD586

GND

NOISE REDUCTION

TRIM

NOTES

1. PINS 1, 3, AND 7 ARE INTERNAL TEST POINTS.

MAKE NO CONNECTIONS TO THESE POINTS.

6

5

4

8

2

Figure 5. Functional Block Diagram

APPLYING THE AD586

The AD586 is simple to use in virtually all precision reference

applications. When power is applied to Pin 2 and Pin 4 is

grounded, Pin 6 provides a 5 V output. No external components

are required; the degree of desired absolute accuracy is achieved

simply by selecting the required device grade. The AD586

requires less than 3 mA quiescent current from an operating

supply of 12 V or 15 V.

An external fine trim may be desired to set the output level to

exactly 5.000 V (calibrated to a main system reference). System

calibration may also require a reference voltage that is slightly

different from 5.000 V, for example, 5.12 V for binary applica-

tions. In either case, the optional trim circuit shown in Figure 6

can offset the output by as much as 300 mV with minimal effect

on other device characteristics.

AD586

GND

1

µF

TRIM

OPTIONAL

NOISE

REDUCTION

CAPACITOR

NOISE

REDUCTION

OUTPUT

10k

Ω

6

5

2

4

8

Figure 6. Optional Fine-Trim Configuration

NOISE PERFORMANCE AND REDUCTION

The noise generated by the AD586 is typically less than 4 µV p-p

over the 0.1 Hz to 10 Hz band. Noise in a 1 MHz bandwidth is

approximately 200 µV p-p. The dominant source of this noise is

the buried Zener, which contributes approximately 100 nV/√Hz.

By comparison, contribution by the op amp is negligible. Figure 7

shows the 0.1 Hz to 10 Hz noise of a typical AD586. The noise

measurement is made with a band-pass filter made of a 1-pole

high-pass filter with a corner frequency at 0.1 Hz, and a 2-pole

low-pass filter with a corner frequency at 12.6 Hz, to create a

filter with a 9.922 Hz bandwidth.

If further noise reduction is desired, an external capacitor can

be added between the noise reduction pin and ground, as

and the Zener resistances, forms a low-pass filter on the output

of the Zener cell. A 1 µF capacitor will have a 3 dB point at

12 Hz, and will reduce the high frequency (to 1 MHz) noise to

about 160 µV p-p. Figure 8 shows the 1 MHz noise of a typical

AD586, both with and without a 1 µF capacitor.

1

µF

5s

1

µF

Figure 7. 0.1 Hz to 10 Hz Noise