Datasheet

Commands
DRDY
SDATAC SYNC RDATAC
SYNC
V
IN
SDATAC
OFSCALor
GANCAL
RDATAC
64DataPeriods
16Data
Periods
Fullystablesignalinputandreferencevoltage.
Calibration
Complete
ADS1281
SBAS378D –AUGUST 2007–REVISED JUNE 2010 www.ti.com
OFSCAL Command
CALIBRATION COMMANDS
The OFSCAL command performs an offset
Calibration commands may be sent to the ADS1281
calibration. Before sending the offset calibration
to calibrate the conversion data. The values of the
command, a zero input signal must be applied to the
offset and gain calibration registers are internally
ADS1281 and the inputs allowed to stabilize. When
written to perform calibration. The appropriate input
the command is sent, the ADS1281 averages 16
signals must be applied to the ADS1281 inputs
readings and then writes this value to the OFC
before sending the commands. Use slower data rates
register. The contents of the OFC register may be
to achieve more consistent calibration results; this
subsequently read or written. During offset
effect is a byproduct of the lower noise that these
calibration, the full-scale correction is bypassed.
data rates provide. Also, if calibrating at power-on, be
sure the reference voltage is fully settled.
GANCAL Command
Figure 51 shows the calibration command sequence.
The GANCAL command performs a gain calibration.
After the analog input voltage (and reference) have
Before sending the GANCAL command sequence
stabilized, send the Stop Data Continuous command
(Figure 51), a dc input must be applied (typically
followed by the SYNC and Read Data Continuous
full-scale input, but not to exceed 103% full-scale).
commands. 64 data periods later, DRDY goes low.
After the signal has stabilized, the command
After DRDY goes low, send the Stop Data
sequence can be sent. The ADS1281 averages 16
Continuous, then the Calibrate command followed by
readings, then computes a gain value that makes the
the Read Data Continuous command. After 16 data
applied input the new full-scale. The gain value is
periods, calibration is complete and conversion data
written to the FSC register, whose contents may be
may be read at this time. The SYNC input must
subsequently read or written.
remain high during the calibration sequence. Note
that calibration is bypassed in sinc filter mode.
Figure 51. Offset/Gain Calibration Timing
28 Submit Documentation Feedback Copyright © 2007–2010, Texas Instruments Incorporated
Product Folder Link(s): ADS1281