Datasheet

AD588
Rev. L | Page 11 of 20
Each AD588 A and B grade unit is tested at −25°C, 0°C, +25°C,
+50°C, +70°C, and +85°C. This approach ensures that the
variations of output voltage that occur as the temperature
changes within the specified range is contained within a box
whose diagonal has a slope equal to the maximum specified
drift. The position of the box on the vertical scale changes from
device to device as initial error and the shape of the curve vary.
Maximum height of the box for the appropriate temperature
range is shown in Figure 13. Duplication of these results
requires a combination of high accuracy and stable temperature
control in a test system. Evaluation of the AD588 produces a
curve similar to that in Figure 12, but output readings may vary,
depending on the test methods and equipment utilized.
AD588JQ
AD588JQ
AD588JQ
AD588JQ
AD588JQ
AD588JQ
DEVICE
GRADE
MAXIMUM OUTPUT CHANGE (mV)
0°C TO +70°C
2.10
1.05
1.40 (TYP)
1.05
3.30
3.30
10.80
7.20
–25°C TO +85°C –55°C TO +125°C
00531-013
Figure 13. Maximum Output Change—mV
KELVIN CONNECTIONS
Force and sense connections, also referred to as Kelvin
connections, offer a convenient method of eliminating the
effects of voltage drops in circuit wires. As seen in Figure 14,
the load current and wire resistance produce an error
(V
ERROR
= R × I
L
) at the load.
The Kelvin connection of Figure 14 overcomes the problem by
including the wire resistance within the forcing loop of the
amplifier and sensing the load voltage. The amplifier corrects
for any errors in the load voltage. In the circuit shown, the
output of the amplifier would actually be at 10 V + V
ERROR
, and
the voltage at the load would be the desired 10 V.
The AD588 has three amplifiers that can be used to implement
Kelvin connections. Amplifier A2 is dedicated to the ground
force-sense function, while uncommitted Amplifier A3 and
Amplifier A4 are free for other force-sense chores.
–
+
10V
R
R
LOAD
R
R
V = 10V
I = 0
I = 0
I
L
V = 10V – RI
L
V = 10V – RI
L
I
L
R
LOAD
00531-014
Figure 14. Advantage of Kelvin Connection
In some single-output applications, one amplifier can be
unused. In such cases, the unused amplifier should be
connected as a unity-gain follower (force and sense pin tied
together), and the input should be connected to ground.
An unused amplifier section can be used for other circuit
functions, as well. Figure 15 through Figure 19 show the typical
performance of A3 and A4.
FREQUENCY (Hz)
100
–20
10 10M100
OPEN-LOOP GAIN (dB)
1k 10k 100k 1M
80
60
40
20
0
0
–180
–30
–60
–90
–120
–150
PHASE (Degrees)
GAIN
PHASE
00531-015
Figure 15. Open-Loop Frequency Response (A3, A4)