AD524 Analog Devices, Inc., AD524 Datasheet - Page 21

• Manufacturer Part Number: AD524
• Description: Precision Instrumentation Amplifier
• Manufacturer: Analog Devices, Inc.

In many applications, complex software algorithms for autozero
applications are not available. For those applications, Figure 51
provides a hardware solution.
INPUTS
DATA
–V
ZERO PULSE
15
WR
CS
S
GND
V
V
14
13
DD
SS
AD589
16
MSB
LSB
39kΩ
200µs
11
12
13
4
2
8
1
RG
RG
+INPUT
–INPUT
2
AD7524
Figure 50. Software Controllable Offset
15
G = 1000
1
A1
G = 100
3
+V
G = 10
RG
14
16
13
12
11
2
3
1
GND
RG
Figure 51. Autozero Circuit
S
2
V
+
–
REF
16
1
AD524
–V
A2
+V
1
2
8
7
S
S
OUT1
OUT2
16
13
12
11
2
3
1
C1
AD711
+
–
10
6
AD524
A3
+V
0.1µF LOW
LEAKAGE
–V
2
3
8
7
S
S
–
+
9
AD712
+V
–
+
1/2
8
S
10
A4
6
1
1kΩ
10kΩ
9
AD7510KD
R4
12
5kΩ
R6
11
R3
20kΩ
5
6
9
–
+
AD712
–V
10
20kΩ
4
1/2
R5
S
V
7
Rev. F | Page 21 of 28
OUT
CH
ERROR BUDGET ANALYSIS
To illustrate how instrumentation amplifier specifications are
applied, review a typical case where an AD524 is required to
amplify the output of an unbalanced transducer. Figure 52
shows a differential transducer, unbalanced by 100 Ω, supplying
a 0 mV to 20 mV signal to an AD524C. The output of the I
feeds a 14-bit ADC with a 0 V to 2 V input voltage range. The
operating temperature range is −25°C to +85°C. Therefore, the
largest change in temperature, ΔT, within the operating range is
from ambient to +85°C (85°C − 25°C = 60°C).
In many applications, differential linearity and resolution are of
prime importance in cases where the absolute value of a variable is
less important than changes in value. In these applications, only
the irreducible errors (45 ppm = 0.004%) are significant. Further-
more, if a system has an intelligent processor monitoring the
analog-to-digital output, the addition of an autogain/autozero
cycle removes all reducible errors and may eliminate the require-
ment for initial calibration. This also reduces errors to 0.004%.
350Ω
350Ω
+10V
350Ω
350Ω
Figure 52. Typical Bridge Application
G = 100
RG
RG
2
1
16
13
12
11
2
3
1
+V
+
–
8
S
AD524C
–V
4
7
10kΩ
S
5
10
6
9
AD524
0V TO 2V
14-BIT
ADC
F.S.
A