Texas Instruments ADS1282, Manual

Page: 30 / 54

Commands
DRDY
SDATAC SYNC RDATAC
SYNC
V
IN
SDATAC
OFSCAL or
GANCAL
RDATAC
64 Data Periods
16 Data
Periods
Fully stable input and reference voltage.
Calibration
Complete
ADS1282
SBAS418I – SEPTEMBER 2007 – REVISED MARCH 2015 www.ti.com
9.29 Calibration Commands Calibration Commands (continued)
Calibration commands may be sent to the ADS1282
9.29.1 OFSCAL Command
to calibrate the conversion data. The values of the
The OFSCAL command performs an offset
offset and gain calibration registers are internally
calibration. Before sending the offset calibration
written to perform calibration. The appropriate input
command sequence ( Figure 60 ), a zero input signal
signals must be applied to the ADS1282 inputs
must be applied to the ADS1282 and the inputs
before sending the commands. Use slower data rates
allowed to stabilize. When the command sequence
to achieve more consistent calibration results; this
( Figure 60 ) is sent, the ADS1282 averages 16
effect is a byproduct of the lower noise that these
readings and then writes this value to the OFC
data rates provide. Also, if calibrating at power-on, be
register. The contents of the OFC register may be
sure the reference voltage is fully settled.
subsequently read or written. During offset
Figure 60 shows the calibration command sequence.
calibration, the full-scale correction is bypassed.
After the analog input voltage (and reference) have
stabilized, send the Stop Data Continuous command
9.29.2 GANCAL Command
followed by the SYNC and Read Data Continuous
The GANCAL command performs a gain calibration.
commands. 64 data periods later, DRDY goes low.
Before sending the GANCAL command sequence
After DRDY goes low, send the Stop Data
( Figure 60 ), a dc input must be applied (typically full-
Continuous, then the Calibrate command followed by
scale input, but not to exceed 103% full-scale). After
the Read Data Continuous command. After 16 data
the signal has stabilized, the command sequence can
periods, calibration is complete and conversion data
be sent. The ADS1282 averages 16 readings, then
may be read at this time. The SYNC input must
computes a gain value that makes the applied input
remain high during the calibration sequence.
the new full-scale. The gain value is written to the
Note that the calibration commands apply to specific
FSC register, whose contents may be subsequently
PGA settings. If the PGA is changed, recalibration is
read or written.
necessary. Calibration is bypassed in the sinc filter
mode.
Figure 60. Offset and Gain Calibration Timing
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