REV. F

–6–

AD587

In some applications, a varying load may be both resistive and

capacitive in nature, or the load may be connected to the AD587

by a long capacitive cable.

Figure 7b displays the output amplifier characteristics driving a

1000 pF, 0 mA to 10 mA load.

AD587

7.0V

1k

Ω

10V

0V

1000pF

Figure 7a. Capacitive Load Transient /Response

Test Circuit

Figure 7b. Output Response with Capacitive Load

LOAD REGULATION

The AD587 has excellent load regulation characteristics. Figure 8

shows that varying the load several mA changes the output by

only a few

µV.

–6

–4

–2

2468

10

LOAD (mA)

0

–500

–1000

500

1000

Figure 8. Typical Load Regulation Characteristics

TEMPERATURE PERFORMANCE

The AD587 is designed for precision reference applications

where temperature performance is critical. Extensive temperature

testing ensures that the device’s high level of performance is

maintained over the operating temperature range.

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; i.e., ppm/

°C. However, because of nonlinearities in

temperature characteristics that originated in standard Zener

references (such as “S” type characteristics), most manufacturers

have begun to use a maximum limit error band approach to

specify devices. This technique involves the measurement of the

output at three or more different temperatures to specify an

output voltage error band.

Figure 9 shows the typical output voltage drift for the AD587L

and illustrates the test methodology. The box in Figure 9 is

bounded on the sides by the operating temperature extremes and

on the top and the bottom by the maximum and minimum output

voltages measured over the operating temperature range. The

slope of the diagonal drawn from the lower left to the upper right

corner of the box determines the performance grade of the device.

10.100

10.000

–20

0

20

40

TEMPERATURE – C

60

80

SLOPE = T.C. =

10

Figure 9. Typical AD587L Temperature Drift

Each AD587J, AD587K, and AD587L grade unit is tested at 0

°C,

25

°C, and 70°C. Each AD587U grade unit is tested at –55°C,

+25

°C, and +125°C. This approach ensures that the variations

of output voltage that occur as the temperature changes within

the specified range will be contained within a box whose diagonal

has a slope equal to the maximum specified drift. The position

of the box on the vertical scale will change from device to device

as initial error and the shape of the curve vary. The maximum

height of the box for the appropriate temperature range and

device grade is shown in Figure 10. Duplication of these results

requires a combination of high accuracy and stable temperature

control in a test system. Evaluation of the AD587 will produce

acurve similar to that in Figure 9, but output readings may vary

depending on the test methods and equipment utilized.

Figure 10. Maximum Output Change in mV