INA104BM BURR-BROWN [Burr-Brown Corporation], INA104BM Datasheet - Page 8

• Manufacturer Part Number: INA104BM
• Description: Very-High Accuracy INSTRUMENTATION AMPLIFIER
• Manufacturer: BURR-BROWN [Burr-Brown Corporation]

OPTIONAL OFFSET ADJUSTMENT
PROCEDURE
It is frequently desirable to null the input component of offset
(Figure 1) and occasionally that of the output (Figure 2). The
quality of the potentiometer will affect the results, therefore,
choose one with good temperature and mechanical-resistance
stability. The procedure is as follows:
1. Set E
2. Set the gain to the desired value (greater than 1) by
3. Adjust the 100k
4. If the output component of offset is to be removed or if it
BASIC CIRCUIT CONNECTION
The basic circuit connection for the INA104 is shown in Figure
1. The output voltage is a function of the differential input
voltage times the gain. Figure 1 does not include additional
internal op amp A
tantalum capacitor or equivalent is always recommended.
In applications which do not use the fourth internal amplifier
(A
to Common and pins 10 and 11 should be connected to-
gether. This will prevent the output of A
(“locking-up”) and affecting the offset of the instrumenta-
tion amplifier, A
FIGURE 2. Optional Output Offset Nulling or Offsetting
4
to the input).
choosing R
output reads 0V 1mV or desired setting. Note that the
offset will change when the gain is changed.
is desired to establish an intentional offset, adjust the
100k potentiometer in Figure 2 until the output reads 0V
change with gain, but be sure to use a stable amplifier with
good DC characteristics. The range of adjustment is 15mV
as shown. For larger ranges, change the ratio of R
The op amp is used to maintain a low resistance (<0.1 )
from pin 6 to Common to avoid CMR degradation.
—pins 7, 9, 10, 11, and 12), pin 7 should be connected
1mV or desired setting. Note that the offset will not
E
E
1
2
1
= E
R
2
G
Using an Amplifier (Low Impedance to Pin 6).
®
17
18
14
= 0V (be sure a good ground return path exists
G
5
1
2
.
INA104
1
+V
–V
–In
+In
, A
4
CC
CC
. Power supply bypassing with a 1 F
3
13
2
, and A
Reference
amp (OPA27 or equivalent) may also be used.
potentiometer in Figure 1 until the
NOTE: (1) A
12
(1)
10
E
E
8
OUT
5k
3
= E
6
.
= (E
6
4
INA104
, internal to the INA104. External
7
2
1k
R
– E
1M
2
R
1
)(1+ 40k/R
1
4
8
from saturating
+15V
–15V
G
E
) + V
100k
OUT
R
3
1
OFFSET
to R
2
.
8
FIGURE 3. Additional Gain From Output Stage.
TYPICAL APPLICATIONS
Many applications of instrumentation amplifiers involve the
amplification of low-level differential signals from bridges
and transducers such as strain gages, thermocouples, and
RTDs. Some of the important parameters include common-
mode rejection (differential cancellation of common-mode
offset and noise), input impedance, offset voltage and drift,
gain accuracy, linearity, and noise. The INA104 accom-
plishes all of these with high precision.
Figure 3 shows how the output stage may be used to provide
additional gain. If gains greater than 1000V/V (10,000 up to
100,000 and greater) are desired, it is better to place some
gain in the output amplifier rather than the input stage due
FIGURE 4. Output Offsetting.
NOTE: (1) A
NOTE: (1) A
pin 8 to pin 10. Therefore, the equation for E
of E
2
E
E
– E
E
E
1
2
1
2
1
.
4
R
4
E
inverts, see Figure 3.
R
G
inverts the output of the Instrumentation Amplifier,
OUT
17
18
14
G
5
1
2
17
18
14
5
1
2
= (E
+V
–V
+V
–V
CC
CC
1
13
3
CC
CC
– E
13
3
INA104
2
)[(1 + (40k/R
–V
INA104
CC
E
OUT
6
6
= (E
R
R = a convenient value
7
G
V
1
7
(<100k typically)
)](R
Output
12
REF
– E
OUT
A3
11
8
8
F
2
+V
/10k)
R
)[1 + (40k/R
shows E
(1)
9
F
(1)
CC
9
10
10
1
– E
G
E
)] + 2V
2
OUT
E
instead
OUT
REF