OPA365 Datasheet, PDF (13/16 Pages) Burr-Brown (TI) – 2.2V, 50MHz, Low-Noise, Single-Supply Rail-to-Rail OPERATIONAL AMPLIFIERS

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Figure 12 illustrates the OPA2365 dual op amp provid-
ing signal conditioning within an ADS1258 bridge sen-
sor circuit. It follows the ADS1258 16:1 multiplexer and
is connected as a differential in/differential out amplifier.
The voltage gain for this stage is approximately 10V/V.
Driving the ADS1258 internal ADC in differential mode,
rather than in a single-ended, exploits the full linearity
performance capability of the converter. For best com-
mon-mode rejection the two R₂ resistors should be
closely matched.
Note that in Figure 12, the amplifiers, bridges,
ADS1258 and internal reference are powered by the
same single +5V supply. This ratiometric connection
helps cancel excitation voltage drift effects and noise.
OPA365
OPA2365
SBOS365A − JUNE 2006 − REVISED JULY 2006
For best performance, the +5V supply should be as free
as possible of noise and transients.
When the ADS1258 data rate is set to maximum and
the chop feature enabled, this circuit yields 12 bits of
noise-free resolution with a 50mV full-scale input.
The chop feature is used to reduce the ADS1258 offset
and offset drift to very low levels. A 2.2nF capacitor is
required across the ADC inputs to bypass the sampling
currents. The 47Ω resistors provide isolation for the
OPA2365 outputs from the relatively large, 2.2nF ca-
pacitive load. For more information regarding the
ADS1258, see the product data sheet available for
down load at www.ti.com.
RFI
2kΩ
RFI
2kΩ
RFI
AIN0
AIN1
2kΩ
RFI
2kΩ
RFI
RFI
AIN14
AIN15
AINCOM
+5V
0.1µF 10µF
AVSS
AVDD
ADS1258
REFP
+ _10µF
REFN
0.1µF
+5V
0.1µF
OPA2365
R₂ = 10kΩ
2.2nF
R₃
47Ω
R₁ = 2.2kΩ
R₂ = 10kΩ
OPA2365
R₃
47Ω
NOTE: G = 1 + 2R₂/R₁. Match R₂ resistors for optimum CMRR.
Figure 12. Conditioning Input Signals to the ADS1258 on a Single-Supply
13