Datasheet

ADS1217
SBAS260C
25
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±V
PGA
REF
5V SUPPLY ANALOG INPUT
(1)
GENERAL EQUATIONS
DIFFERENTIAL PGA OFFSET FULL-SCALE DIFFERENTIAL PGA SHIFT
GAIN SETTING FULL-SCALE RANGE INPUT VOLTAGES
(2)
RANGE RANGE INPUT VOLTAGES
(2)
RANGE
1 10V ±5V ±2.5
25V±2.5V ±1.25V
42.5V±1.25V ±0.625V
8 1.25V ±0.625V ±312.5mV
16 0.625V ±312.5mV ±156.25mV
32 312.5mV ±156.25mV ±78.125mV
64 156.25mV ±78.125mV ±39.0625mV
128 78.125mV ±39.0625mV ±19.531mV
NOTES: (1) With a 2.5V reference. (2) The ADS1217 allows common-mode voltage as long as the absolute input voltage on A
IN+
or A
IN–
does not go below
AGND or above AV
DD
.
TABLE V. Full-Scale Range versus PGA Setting.
Full-Scale Range (FSR)—as with most A/D converters, the
full-scale range of the ADS1217 is defined as the “input”,
which produces the positive full-scale digital output minus the
“input”, which produces the negative full-scale digital output.
The full-scale range changes with gain setting, see Table V.
For example, when the converter is configured with a 2.5V
reference and is placed in a gain setting of 2, the full-scale
range is: 2 • [1.25V (positive full-scale) minus –1.25V (nega-
tive full-scale)] = 5V.
Least Significant Bit (LSB) Weight—this is the theoretical
amount of voltage that the differential voltage at the analog
input would have to change in order to observe a change in
the output data of one least significant bit. It is computed as
follows:
LSB Weight
Full Scale Range
N
=
−
2
where N is the number of bits in the digital output.
t
DATA
—the inverse of f
DATA
, or the period between each data
output.
4V
PGA
REF
±2V
PGA
REF