INA104BM BURR-BROWN [Burr-Brown Corporation], INA104BM Datasheet - Page 9

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

FIGURE 5. Use of Guard Drive.
FIGURE 6. Active Low-Pass Filtering.
to the low values of R
> 1000). Note, however, that accuracy can degrade due to
high amplification of offset, drift, and noise errors.
Output offsetting (“zero suppression” or “zero elevation”)
may be more easily accomplished with the INA104 than
with most other IC instrumentation amplifiers as shown in
Figure 4. The use of the extra internal op amp, A
that CMR of the instrumentation amp is not disturbed, and
that a convenient value of variable resistor can be used. The
circuit shown in Figure 2 can also be used to achieve the
desired offsetting by scaling the resistors R
impedance path from pin 6 to Common should be provided
to achieve the high CMR specified. Resistance above 0.1
will cause the CMR to fall below 106dB.
NOTE: Internal Op Amp, A
E
E
1
2
(f)
(f)
E
R
OUT
17
18
14
G
5
1
2
= (E
+V
–V
1
CC
CC
13
3
– E
G
required (R
2
INA104
)[1 + (40k/R
4
, or External Amp (OPA27 or equivalent).
E
1
NOTE: (1) A
6
E
CM
C
F
E
G
in farads used with A
12
f
7
2
)][1/(1 + 2 f 10
P
G
= (1/2 C
< 40 for (1 + 40k/R
8
11
4
Shield
C
inverts, see Figure 3.
(1)
9
F
F
10
1
and R
4
10
4
)Hz
x C
F
4
)]
4
.
2
, means
. A low
E
OUT
R
G
G
)
17
18
14
5
1
2
9
+V
–V
–In
+In
CC
CC
13
3
FIGURE 7. Output Power Boosting.
Amplifier A
implemented conveniently with a single capacitor. Filtering
can be used for noise reduction or band-limiting of the
output signal as shown in Figure 6.
The common-mode voltage from the 26k
input section appears at pin 4. Figure 5 shows how this
voltage can be used to drive the shield of the input cable.
Since the cable is driven at the common-mode voltage, the
effects of distributed capacitance is reduced and the AC
system common-mode rejection may be improved. Ampli-
fier A
Some typical application circuits are shown in Figures 9
through 11.
12
(1)
E
E
4
1
2
10
NOTE: (1) A
buffers the CMV at pin 4 from the input cable.
5k
R
6
G
E
INA104
4
17
18
14
OUT
5
1
2
7
also allows active low-pass filtering to be
= [E
+V
–V
4
4
inverts. See Figure 3.
CMV Sense
CC
CC
13
3
2
– E
8
INA104
1
+ (E
CM
6
E
OUT
/CMRR)](1 + 40k/R
7
INA104
11
8
(1)
9
10
G
resistors in the
)
3553 or BUF634
Current Booster
Used with A
E
OUT
4
®