Data Sheet
AD588
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.
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.
R
I = 0
V = 10V
R
V = 10V – RI
R
L
R
+
–
I
L
LOAD
R
I = 0
10V
LOAD
I
L
V = 10V – RI
L
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.
DEVICE MAXIMUM OUTPUT CHANGE (mV)
GRADE
0°C TO +70°C –25°C TO +85°C
AD588J
AD588K
AD588A
AD588B
2.10
1.05
1.40 (TYP)
1.05
3.30
3.30
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.
Figure 13. Maximum Output Change—mV
100
80
60
40
20
0
0
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
(VERROR = R × IL) at the load.
–30
–60
–90
–120
–150
–180
GAIN
PHASE
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 + VERROR, and
the voltage at the load would be the desired 10 V.
–20
10
100
1k
10k
100k
1M
10M
FREQUENCY (Hz)
Figure 15. Open-Loop Frequency Response (A3, A4)
Rev. M | Page 11 of 20
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