8.4.12 Calibration Commands (OFSCAL and GANCAL)

Use the calibration commands (OFSCAL or GANCAL) to calibrate the conversion data. The values of the offset and gain calibration registers are internally written to perform calibration. The appropriate input signals must be applied to the ADS1284 inputs before sending the commands. Use slower data rates to achieve more consistent calibration results; this effect is a byproduct of the lower noise that these data rates provide. Also, if calibrating at power-on, be sure the reference voltage is fully settled.

Figure 65 shows the calibration command sequence. After the analog input voltage (and reference) have stabilized, send the SDATAC command, followed by the SYNC and RDATAC commands. DRDY goes low after 64 data periods. After DRDY goes low, send the SDATAC command, then the calibrate command (OFSCAL or GANCAL), followed by the RDATAC command. After 16 data periods, calibration is complete and conversion data can be read at this time. The SYNC input must remain high during the calibration sequence.

Figure 65. Offset and Gain Calibration Timing

The calibration commands apply to specific PGA settings. If the PGA is changed, recalibration is necessary. Calibration is bypassed in the sinc filter mode.