Analog-to-Digital Converter
C2000 Microcontroller Workshop - Analog-to-Digital Converter 6 - 15
ADC Calibration and Reference
Built-In ADC Calibration
TI reserved OTP contains device specific calibration data
for the ADC and internal oscillators
The Boot ROM contains a Device_cal() routine that copies
the calibration data to their respective registers
Device_cal() must be run to meet the ADC and oscillator
specs in the datasheet
The Bootloader automatically calls Device_cal() such that no
action is normally required by the user
If the Bootloader is bypassed (e.g., during development)
Device_cal() should be called by the application:
A GEL function using CCS is also available as part of the
Peripheral Register Header Files to accomplish this
#define Device_cal (void (*)(void))0x3D7C80
void main(void)
{
(*Device_cal)(); // call Device_cal()
}
Manual ADC Calibration
If the offset and gain errors in the datasheet* are unacceptable for your
application, or you want to also compensate for board level errors (e.g.,
sensor or amplifier offset), you can manually calibrate
Offset error
Compensated in analog with
the ADCOFFTRIM register
No reduction in full-scale range
Configure input B5 to VREFLO, set
ADCOFFTRIM to maximum offset
error, and take a reading
Re-adjust ADCOFFTRIM to
make result zero
Gain error
Compensated in software
Some loss in full-scale range
Requires use of a second ADC input pin and an upper-range reference
voltage on that pin; see “TMS320280x and TMS320F2801x ADC Calibration”
appnote #SPRAAD8 for more information
Tip: To minimize mux-to-mux variation effects, put your most critical
signals on a single mux and use that mux for calibration inputs
* +/-15 LSB offset, +/-30 LSB gain. See device datasheet for exact specifications
C
H
C
H
MUX
VREFLOCONV
VREFLO
B5
ADCOFFTRIM
12-bit
ADC
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