LT1996 Linear Technology, LT1996 Datasheet - Page 13

• Manufacturer Part Number: LT1996
• Description: 100uA Gain Selectable Amplifier
• Manufacturer: Linear Technology

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APPLICATIO S I FOR ATIO
Attenuation Using the P Input Resistors
Attenuation happens as a matter of fact in difference
amplifier configurations, but it is also used for reducing
peak signal level or improving input common mode range
even in single ended systems. When signal conditioning
indicates a need for attenuation, the LT1996 resistors are
ready at hand. The four precision resistors can provide
several attenuation levels, and these are tabulated in
Table 2 as a design reference.
Because the attenuations and the noninverting gains are
set independently, they can be combined. This provides
high gain resolution, about 700 unique gains between
0.0085 and 118, as plotted in Figure 7. This is too large a
number to tabulate, but the designer can calculate achiev-
able gain by taking the vector product of the gains and
attenuations in Tables 1 and 2, and seeking the best match.
Average gain resolution is 1.5%, with worst case steps of
about 50% as seen in Figure 7.
Figure 6. LT1996 Provides for Easy Attenuation to the Op Amp’s
+Input. The P9 Input Can Be Taken Well Outside of the Supplies
4
Figure 7. Over 600 Unique Gain Settings Achievable with the
LT1996 by Combining Attenuation with Noninverting Gain
V
CLASSICAL ATTENUATOR
IN
R
R
G
A
V
INT
V
A = R
0.001
1000
0.01
INT
100
0.1
10
1
= A • V
G
/(R
0
OKAY UP
TO ±60V
A
+ R
IN
U
100
V
G
IN
)
200
U
300
1
2
3
DRIVING AND GROUNDING AND FLOATING
COUNT
LT1991 ATTENUATING TO THE +INPUT BY
INPUTS R
450k/27
450k/81
450k/9
400
A
500
= 50k, R
W
V
INT
600
G
1996 F07
450k
+
= 50k/9, SO A = 0.1.
700
5
LT1996
U
1996 F06
Table 2. Configuring the P Pins for Various Attenuations. Those
Shown in Bold Are Functional Even When the Input Drive
Exceeds the Supplies
0.0085
0.0092
0.0110
0.0122
0.0270
0.0357
0.0763
0.0769
0.0847
0.0989
0.110
0.229
0.231
0.237
0.243
0.248
0.257
0.270
0.305
0.308
0.314
0.686
0.692
0.695
0.730
0.743
0.752
0.757
0.763
0.769
0.771
0.890
0.901
0.915
0.923
0.924
0.964
0.973
0.988
0.989
0.991
0.992
0.25
0.25
0.75
0.1
0.9
A
Grounded
Grounded
Grounded
Grounded
Grounded
Grounded
Grounded
Grounded
Grounded
Grounded
Grounded
Grounded
Grounded
Grounded
Grounded
Grounded
Grounded
Grounded
Grounded
Driven
Driven
Driven
Driven
Driven
Driven
Driven
Driven
Driven
Driven
Driven
Driven
Driven
Driven
Driven
Driven
Driven
Float
Float
Float
Float
Float
Float
Float
Float
Float
Float
Float
P81
P81, P27, P9, REF Connection
Grounded
Grounded
Grounded
Grounded
Grounded
Grounded
Grounded
Grounded
Grounded
Grounded
Grounded
Grounded
Grounded
Grounded
Grounded
Grounded
Grounded
Grounded
Driven
Driven
Driven
Driven
Driven
Driven
Driven
Driven
Driven
Driven
Driven
Driven
Driven
Driven
Driven
Driven
Driven
Driven
Driven
Float
Float
Float
Float
Float
Float
Float
Float
Float
Float
P27
Grounded
Grounded
Grounded
Grounded
Grounded
Grounded
Grounded
Grounded
Grounded
Grounded
Grounded
Grounded
Grounded
Grounded
Grounded
Grounded
Grounded
Driven
Driven
Driven
Driven
Driven
Driven
Driven
Driven
Driven
Driven
Driven
Driven
Driven
Driven
Driven
Driven
Driven
Driven
Driven
Float
Float
Float
Float
Float
Float
Float
Float
Float
Float
Float
P9
LT1996
Grounded
Grounded
Grounded
Grounded
Grounded
Grounded
Grounded
Grounded
Grounded
Grounded
Grounded
Grounded
Grounded
Grounded
Grounded
Grounded
Grounded
Grounded
Grounded
Driven
Driven
Driven
Driven
Driven
Driven
Driven
Driven
Driven
Driven
Driven
Driven
Driven
Driven
Driven
Driven
Driven
Driven
13
Float
Float
Float
Float
Float
Float
Float
Float
Float
Float
REF
1996f