AD588TQ Analog Devices, AD588TQ Datasheet - Page 7

• Manufacturer Part Number: AD588TQ
• Description: High Precision Voltage Reference
• Manufacturer: Analog Devices

additional load to the internal Zener diode’s current source,
resulting in a somewhat longer turn-on time. In the case of a
1 µF capacitor, the initial turn-on time is approximately 60 ms
(see Figure 6).
Note: If the NOISE REDUCTION feature is used in the ± 5 V
configuration, a 39 kΩ resistor between Pin 6 and Pin 2 is required
for proper startup.
TEMPERATURE PERFORMANCE
The AD588 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.
Figure 7 shows typical output voltage drift for the AD588BD
and illustrates the test methodology. The box in Figure 7 is
bounded on the sides by the operating temperature extremes
and on top and bottom by the maximum and minimum output
voltages measured over the operating temperature range. The
slope of the diagonal drawn from the lower left corner of the
box determines the performance grade of the device.
OUTPUT
Each AD588A 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 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. Maxi-
mum height of the box for the appropriate temperature range is
shown in Figure 8. Duplication of these results requires a combi-
nation of high accuracy and stable temperature control in a test
system. Evaluation of the AD588 will produce a curve similar to
that in Figure 7, but output readings may vary depending on the
test methods and equipment utilized.
REV. D
10.001
10.000
10.002
VOLTS
V
V
MAX
MIN
Figure 7. Typical AD588BD Temperature Drift
–35 –15
T
min
Figure 6. Turn-On with C
TEMPERATURE – C
5
25
45
65
T
85
max
SLOPE
=
T.C. =
N
= 1 F
(85 C –25 C)
=
10.0013V 10.00025V
0.95ppm / C
° −
(T
MAX
– T
V
°
MAX
MIN
−
°
)
– V
×
×
10
MIN
10
×
×
10
1
–6
–6
–7–
KELVIN CONNECTIONS
Force and sense connections, also referred to as Kelvin connec-
tions, offer a convenient method of eliminating the effects of
voltage drops in circuit wires. As seen in Figure 9, the load
current and wire resistance produce an error (V
the load. The Kelvin connection of Figure 9 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
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 amplifiers A3 and A4
are free for other force-sense chores.
In some single-output applications, one amplifier may be unused.
In such cases, the unused amplifier should be connected as a
unity-gain follower (force + sense pin tied together), and the
input should be connected to ground.
An unused amplifier section may be used for other circuit functions
as well. Figures 10 through 14 show the typical performance of
A3 and A4.
Figure 10. Open-Loop Frequency Response (A3, A4)
100
–20
80
60
40
20
10V
0
10
Figure 9. Advantage of Kelvin Connection
Figure 8. Maximum Output Change—mV
AD588JQ
AD588JQ
AD588JQ
AD588JQ
AD588JQ
AD588JQ
+
–
DEVICE
GRADE
R
I
100
L
V = 10V – RI
0 C TO +70 C
R
PHASE
1.40(typ)
LOAD
1.05
2.10
1.05
1k
MAXIMUM OUTPUT CHANGE – mV
GAIN
FREQUENCY – Hz
L
10k
–25 C TO +85 C –55 C TO +125 C
I = 0
R
3.30
3.30
100k
V = 10V + RI
I = 0
R
ERROR
1M
10.80
7.20
I
L
L
AD588
= R × I
V = 10V
R
10M
LOAD
ERROR
0
–150
–30
–60
–90
–120
–180
L
) at
and