Texas Instruments ADS1282V2EVM-PDK User Manual page 5

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2.2 Common-Mode Amplifier
Figure 2-2 shows the OPA379
requires from the input signals. The circuit output, Vocm, provides a voltage that is mid-scale with respect to the
selected input range of the ADS1282. In unipolar mode, Vocm is +2.5V relative to ground. In bipolar mode, Vocm
is 0V relative to ground.
Vref
R54
10.0k
R56
10.0k
AVSS
2.3 Analog Input 1 Circuit
Figure 2-3 shows the front-end circuit to ADC input channel 1. Vocm supplies a DC shift to the differential inputs
connected to header J3. In unipolar mode, differential-output sources with a common-mode voltage equal to
ground (0V) are given a +2.5V DC shift. The DC shift raises the input signal common-mode voltage by the same
amount (2.5V), and the signal at the inputs to the ADS1282 has a common-mode voltage close to mid-scale of
the unipolar input range (0-5V). The mid-scale common-mode voltage makes analog input channel 1 best for
bipolar differential signals centered around a 0V common-mode voltage.
J3
SBAU431 – JULY 2024
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op-amp circuit used to generate the common-mode voltage that the ADS1282
R52
10.0k
R53
10.0k
AVDD(5.3)
C27
0.1uF
AVSS
3
1
C28
1µF
AVSS AVSS
Figure 2-2. Common-Mode Amplifier
-AIN1
R5
20.0k
3
2
1
GND
R6
20.0k
+AIN1
Figure 2-3. Analog Input 1 Circuit
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C26
0.033 µF
R55
4
37.4
U6
C29
OPA379AIDCKT
10µF
AVSS
R3 R4
221 221
C5
1000pF
Vocm
C7
1000pF
R7 R8
221 221
Hardware
TP9
Vocm
Vocm
AINN1
C6
0.01 µF
AINP1
ADS1282EVM-PDK Evaluation Module 5