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 7 displays the output amplifier characteristics driving a
1000 pF, 0 mA to 10 mA load.
Some confusion exists in the area of defining and specifying ref-
erence voltage error over temperature. Historically, references
have been characterized using a maximum deviation per degree
Centrigrade; i.e., ppm/°C. However, because of nonlinearities in
temperature characteristics which originated in standard Zener
references (such as “S” type characteristics), most manufactur-
ers 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 out-
put 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 thc 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.
V
OUT
7.0V
C
L
1000pF
1kΩ
AD587
V
L
10V
0V
Figure 7a. Capacitive Load Transient /Response Test Circuit
Figure 7b. Output Response with Capacitive Load
LOAD REGULATION
Figure 9. Typical AD587L Temperature Drift
The AD587 has excellent load regulation characteristics. Figure
8 shows that varying the load several mA changes the output by
only a few
µV.
Each AD587J, K, L grade unit is tested at 0°C, +25°C and
+70°C. Each AD587S, T, and U 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 diago-
nal has a slope equal to the maximum specified drift. The posi-
tion of the box on the vertical scale will change from device to
device as initial error and the shape of the curve vary. The maxi-
mum 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 a curve similar to that in Figure 9, but output
readings may vary depending on the test methods and equip-
ment utilized.
Figure 8. Typical Load Regulation Characteristics
TEMPERATURE PERFORMANCE
The AD587 is designed for precision reference applications
where temperature performance is critical. Extensive tempera-
ture testing ensures that the device’s high level of performance is
maintained over the operating temperature range.
–6–
Figure 10. Maximum Output Change in mV
REV. D
AD [ ANALOG DEVICES ]
