ADS8671 Datasheet, PDF (31/72 Pages) Texas Instruments – 14-Bit, High-Speed, Single-Supply, SAR ADC Data Acquisition System with Programmable, Bipolar Input Ranges

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ADS8671, ADS8675
SBAS779 – DECEMBER 2016
7.3.8 ADC Transfer Function
The device supports a pseudo-differential input supporting both bipolar and unipolar input ranges. The output of
the device is in straight-binary format for both bipolar and unipolar input ranges.
The ideal transfer characteristic for all input ranges is shown in Figure 64. The full-scale range (FSR) for each
input signal is equal to the difference between the positive full-scale (PFS) input voltage and the negative full-
scale (NFS) input voltage. The LSB size is equal to FSR / 2¹⁴. For a reference voltage of V_REF = 4.096 V, the
LSB values corresponding to the different input ranges are listed in Table 4.
3FFFh
2000h
0001h
NFS
1 LSB
FSR / 2
FSR ± 1 LSB
Analog Input
PFS
(AIN_P ± AIN_GND)
Figure 64. Device Transfer Function (Straight-Binary Format)
INPUT RANGE
±3 × V_REF
±2.5 × V_REF
±1.5 × V_REF
±1.25 × V_REF
±0.625 × V_REF
0 to 3 × V_REF
0 to 2.5 × V_REF
0 to 1.5 × V_REF
0 to 1.25 × V_REF
Table 4. ADC LSB Values for Different Input Ranges (V_REF = 4.096 V)
POSITIVE FULL-SCALE NEGATIVE FULL-SCALE FULL-SCALE RANGE
(V)
(V)
(V)
12.288
–12.288
24.576
10.24
–10.24
20.48
6.144
–6.144
12.288
5.12
–5.12
10.24
2.56
–2.56
5.12
12.288
0
12.288
10.24
0
10.24
6.144
0
6.144
5.12
0
5.12
LSB
1.5 mV
1.25 mV
0.75 mV
0.625 mV
0.312 mV
0.75 mV
0.625 mV
0.375 mV
0.312 mV
Copyright © 2016, Texas Instruments Incorporated
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