Datasheet

www.ti.com
LSB Weight +
Full−Scale Range
2
N
(1)
2V
REF
PGA
" V
REF
PGA
" V
REF
2PGA
ADS1216
SBAS171D – NOVEMBER 2000 – REVISED SEPTEMBER 2006
Filter Selection—the ADS1216 uses a (sinx/x) filter For example, when the converter is configured with a
or sinc filter. There are three different sinc filters that 2.5V reference and is placed in a gain setting of 2,
can be selected. A Fast-Settling filter will settle in the full-scale range is: [1.25V (positive full-scale) –
one t
DATA
cycle. The Sinc
2
filter will settle in two (–1.25V (negative full-scale))] = 2.5V.
cycles and have lower noise. The Sinc
3
will achieve
Least Significant Bit (LSB) Weight—this is the
lowest noise and higher number of effective bits, but
theoretical amount of voltage that the differential
requires three cycles to settle. The ADS1216 will
voltage at the analog input would have to change in
operate with any one of these filters, or it can
order to observe a change in the output data of one
operate in an auto mode, where it will first select the
least significant bit. It is computed as shown in
Fast-Settling filter after a new channel is selected for
Equation 1 :
two readings and will then switch to Sinc
2
for one
reading, followed by Sinc
3
from then on.
Full-Scale Range (FSR)—as with most A/D
where N is the number of bits in the digital output.
converters, the full-scale range of the ADS1216 is
defined as the input, which produces the positive
t
DATA
—the inverse of f
DATA
, or the period between
full-scale digital output minus the input, which
each data output.
produces the negative full-scale digital output. The
full-scale range changes with gain setting; see
Table 5 .
Table 5. Full-Scale Range vs PGA Setting
5V SUPPLY ANALOG INPUT
(1)
GENERAL EQUATIONS
DIFFERENTIAL DIFFERENTIAL
GAIN FULL-SCALE INPUT PGA OFFSET FULL-SCALE INPUT PGA SHIFT
SETTING RANGE VOLTAGES
(2)
RANGE RANGE VOLTAGES
(2)
RANGE
1 5V ± 2.5V ± 1.25V
2 2.5V ± 1.25V ± 0.625V
4 1.25V ± 0.625V ± 312.5mV
8 0.625V ± 312.5mV ± 156.25mV
16 312.5mV ± 156.25mV ± 78.125mV
34 156.25mV ± 78.125mV ± 39.0625mV
64 78.125mV ± 39.0625mV ± 19.531mV
128 39.0625mV ± 19.531mV ± 9.766mV
(1) With a 2.5V reference.
(2) The ADS1216 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
.
33
Submit Documentation Feedback