ADIN0
ADIN31
Self-test and
calibration
AD
REFLO
AD
REFHI
V
in
R1
R2
S4
S1 S2
S3
S5
ADC Core
ADDRx.16,9:0
ADCALR.9:0
CALR
MUX
R1 ~ 5K
R2 ~ 7K
Basic Operation
871
SPNU563A – March 2018
Copyright © 2018, Texas Instruments Incorporated
Analog To Digital Converter (ADC) Module
22.2.6 ADC Special Modes
The ADC module supports some special modes for diagnostics and power saving purposes.
22.2.6.1 ADC Error Calibration Mode
The application program can activate a calibration sequence any time self-test mode is disabled
(SELF_TEST = 0). This calibration sequence includes the conversion of an embedded calibration
reference voltage followed by the calculation of an offset error correction value.
NOTE:
Disable Self-Test Mode Before Calibration
To avoid errors during the calibration operation, self-test mode must
not
be enabled during a
calibration sequence. In addition, to ensure accurate results, calibrate the ADC in an
environment with minimum noise.
Calibration mode is enabled by setting the CAL_EN bit (ADCALCR.0). The application needs to ensure
that no conversion group is being serviced when the calibration mode is enabled.
The input multiplexor gets disabled and only the reference voltage is connected to the ADC core input.
Switch S5 of
is opened. In addition, the digital result issued from a conversion is output from
the ADC core to the calibration and offset error correction register, ADCALR. The ADC results’ memory is
not affected by the calibration conversion.
When calibration mode is disabled, the ADC can be configured for normal conversions.
Figure 22-13. Self-Test and Calibration Logic
22.2.6.1.1 Calibration Conversion
The calibration conversion also needs to meet the minimum sampling time specification for the ADC. This
value is typically 1 us. The Event Group sample time register (ADEVSAMP) is used to specify the number
of ADCLK cycles for the calibration conversion.
The BRIDGE_EN and HILO bits (ADCALCR.9:8) control the voltage to the calibration reference device
shown in
. The positions of the switches in calibration mode are listed in
.