LT1997-2
16
Rev 0
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APPLICATIONS INFORMATION
Difference Amplifier: Additional Gains Using Cross-
Coupling
Figure 5 shows the basic difference amplifier as well as
the LT1997-2 with cross-coupled inputs. The additional
dashed connections reduce the differential gain from 0.25
to 0.15. Using this method, additional gains are achievable
and a few example schematics of the difference amplifiers
using cross-coupling are shown in Figure 6. To summarize,
Table1 shows a complete list of all difference amplifier
gains (attenuations) and how they are constructed using
(both conventional or cross-coupling) pin strapping.
Note that there are 38 unique gains ranging from 0.0455
to 0.55 (corresponding to attenuations from 1.8182 to
22) which can be achieved with the LT1997-2 using no
external components.
Table1. Difference Amplifier Gains (Attenuations)
GAIN ATTENUATION V+IN V–IN GND (REF) OUT
0.0455 22 –INB, +INC +INB, –INC +INA –INA
0.05 20 –INB, +INC +INB, –INC
0.0556 18 –INB, +INC +INB, –INC –INA +INA
0.069 14.5 +INA –INA +INB, +INC –INB, –INC
0.08 12.5 +INA –INA +INC –INC
0.0833 12 +INA –INA +INB –INB
0.0952 10.5 +INA –INA –INB, +INC +INB, –INC
0.1 10 +INA –INA
0.1053 9.5 +INA –INA +INB, –INC –INB, +INC
0.125 8 +INA –INA –INB +INB
0.1333 7.5 +INA –INA –INC +INC
0.1481 6.75 +INB –INB +INA, +INC –INA, –INC
0.15 6.6667 –INA, +INC +INA, –INC
0.16 6.25 +INB –INB +INC –INC
0.1739 5.75 +INB –INB –INA, +INC +INA, –INC
0.1818 5.5 +INB –INB +INA –INA
0.1875 5.3333 –INA, +INC +INA, –INC –INB +INB
0.1923 5.2 +INC –INC +INA, +INB –INA, –INB
0.2 5 +INB –INB
0.2083 4.8 +INC –INC +INB –INB
0.2222 4.5 +INB –INB –INA +INA
0.2273 4.4 +INC –INC +INA –INA
0.24 4.1667 +INA, +INB –INA, –INB +INC –INC
0.25 4 +INC –INC
0.2667 3.75 +INB –INB –INC +INC
0.2778 3.6 +INC –INC –INA +INA
0.2917 3.4286 +INA, +INC –INA, –INC +INB –INB
0.3 3.3333 +INA, +INB –INA, –INB
0.3077 3.25 +INB –INB –INA, –INC +INA, +INC
0.3125 3.2 +INC –INC –INB +INB
0.35 2.8571 +INA, +INC –INA, –INC
0.3571 2.8 +INC –INC –INA, –INB +INA, +INB
0.4 2.5 +INA, +INB –INA, –INB –INC +INC
0.4091 2.4444 +INB, +INC –INB, –INC +INA –INA
0.4375 2.2857 +INA, +INC –INA, –INC –INB +INB
0.45 2.2222 +INB, +INC –INB, –INC
0.5 2 +INB, +INC –INB, –INC –INA +INA
0.55 1.8182 +INA, +INB,
+INC
–INA, –INB,
–INC
Figure 5. Cross-Coupling of the LT1997-2 Allows Additional
Gains to Be Constructed
19972 F05
OUT
REF
250k
250k
100k
125k 25k
125k
100k
25k
–INA –INB –INC
+INA +INB +INC V–
V+
SHDN
–
+
VS+
VS–
VOUT
–IN
+IN
V–IN
V+IN
RG
F
+
–
VOUT
RG
RF
DIFFERENCE AMPLIFIER CONFIGURATION
DIFFERENCE AMPLIFIER CONFIGURATION
IMPLEMENTED WITH THE LT1997-2, RF = 25k, RG = 100k, GAIN = 0.25
GAIN CAN BE ADJUSTED BY CROSS-COUPLING THE INPUTS.
MAKING THE DASHED CONNECTIONS REDUCES THE GAIN FROM 0.25 TO 0.15
VOUT = GAIN • (V+IN – V–IN)
GAIN = RF/RG
LT1997-2