Data Sheet

NAU7802 24-bit ADC
Nuvoton Confidential - 20 - Revision 1.7
8.6 Device Calibration Features
Calibration is not required for low accuracy applications, but may be needed in sensitive
applications. When calibration is used the system designer has three options.
Calibration can be performed at the system level with an external processor or at the ADC
device. Inside the ADC device both internal and external calibration can be performed.
Internal ADC device calibration only removes internal PGA gain and offset errors.
External ADC device calibration removes DC errors at the device input pins and the internal
PGA gain and offset errors.
As with all devices of this type, the NAU7802 internal gain factors and offset voltages will
contain small errors owing to fabrication process variations, power supply voltage changes,
and temperature variations. The same types of errors exist at the external system level.
These errors can be measured by the NAU7802 device itself using the calibration features.
After calibration, the stored values in the calibration registers are automatically
added/subtracted to the data from the ADC before being output as the ADC resulting data. It
is recommended to calibrate the NAU8702 after the following conditions:
 Initial power-up
 Power-up after long-duration register mediated power-down conditions
 PGA gain changes
 Supply changes
 Significant temperature changes (can be measured using built-in thermal sensing feature)
 Sample rate changes
 Channel select changes
Calibration is initiated by writing Logic=1 to R0x02 Bit 2. Bit 2 named “CALS” then
becomes a status bit that can be read to know when calibration is complete. Internal or
external calibration is performed on the Gain or Offset value and input channel as selected by
other bits in R0x02. Bit 2 will remain Logic=1 until calibration is complete, and will read
back as Logic=0 when calibration is completed.
After calibration, it is important to check the CAL_ERR status bit to determine if there was
any problem during calibration. If there was an error, all data output could be invalid.
8.6.1 Internal or External calibration
The internal calibration disconnects the inputs from the input pins and internally connects the
differential inputs to the same internal voltage reference point for calibration. the internal
inputs for offset calibration. External calibration uses the inputs as-is, and it is up to the
system designer to configure them appropriately for the calibration procedure. The resulting
gain or offset calibration value is stored in the selected calibration register. The same register
sets are used for both internal or external calibration and it is intended that only one choice of
internal/external calibration is used at any given time.