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.
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.
T
MIN
10.100
T
MAX
SLOPE = T.C. =
V
MAX
– V
MIN
(T
MAX
– T
MIN
)
V
MAX
10
10
6
V
OUT
7.0V
C
L
1000pF
1kΩ
AD587
V
L
10V
0V
Figure 7a. Capacitive Load Transient /Response
Test Circuit
V
MIN
Figure 7b. Output Response with Capacitive Load
LOAD REGULATION
10.000
–20
0
The AD587 has excellent load regulation characteristics. Figure 8
shows that varying the load several mA changes the output by
only a few
µV.
V
OUT
( V)
20
40
60
TEMPERATURE – C
80
Figure 9. Typical AD587L Temperature Drift
1000
500
2
–6
–4
–2
0
–500
–1000
4
6
8
10
LOAD (mA)
Figure 8. Typical Load Regulation Characteristics
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
a curve 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
–6–
REV. F
AD [ ANALOG DEVICES ]
