AD581

Rev. C | Page 6 of 12

APPLYING THE AD581

The AD581 is easy to use in virtually all precision reference

applications. The three pins are simply: primary supply, ground,

and output, with the case grounded. No external components

are required even for high precision applications; the degree of

desired absolute accuracy is achieved simply by selecting the

required device grade. The AD581 requires less than 1 mA quies-

cent current from an operating supply range of 13 V to 30 V.

GND

AD581

10V

13V TO 30V

Figure 2. Pin Configuration (Bottom View)

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

exactly 10.000 V within less than a millivolt (calibrated to a

main system reference). System calibration may also require a

reference slightly different from 10.00 V. In either case, the

optional trim circuit shown in Figure 3 can offset the output by

up to ±30 mV (with the 22 Ω resistor), if needed, with minimal

effect on other device characteristics.

6.8k

Ω

10k

Ω

4.3k

Ω

GND

AD581

+10V

R

+15V

–15V

R

TRIM

RANGE

MAX

Δ TCR

22

Ω

±30mV

3.5ppm/°C

12

Ω

±10mV

2.0ppm/°C

3.9

Ω

±5mV

0.6ppm/°C

Figure 3. Optional Fine Trim Configuration

V+

10V

V–

Q12

Q14

Q11

Q20

C52

Q6

Q16

Q13

C50

C51

Q10

R40

R41

Q7

Q8

Q15

R42

R34

R37

R35

R36

R30

R31

R39

Q4

Q3

Q5

Q1

Q2

R32

R33

Figure 4. Simplified Schematic

VOLTAGE VARIATION vs. TEMPERATURE

Some confusion exists in the area of defining and specifying

reference voltage error over temperature. Historically, references

have been characterized using a maximum deviation per degree

Celsius; that is, 10 ppm/°C. However, because of nonlinearities

in temperature characteristics, which originated in standard

Zener references (such as S-type characteristics) manufacturers

opt for the maximum limit error band approach to specify devices.

This technique involves measurement of the output at three,

five, or more different temperatures to guarantee that the output

voltage falls within the given error band. The temperature charac-

teristic of the AD581 consistently follows the S-curve shown in

Figure 5. Three-point measurement of each device guarantees

the error band over the specified temperature range.

10.005

9.995

TEMPERATURE (°C)

10.000

–50

–55

–40 –30 –20 –10 0

10 20 30 40 50 60 70 80 90 100 110 120 125

Figure 5. Typical Temperature Characteristic