15
15
15
1
ADC(corrected)
ADC(raw) CAL _ ADC12VREF _ FACTOR
2
1
ADC(corrected)
ADC(raw) CAL _ ADC20VREF _ FACTOR
2
1
ADC(corrected)
ADC(raw) CAL _ ADC25VREF _ FACTOR
2
=
´
´
=
´
´
=
´
´
15
REF
15
REF
15
REF
V
CAL _ ADC _12VREF _ FACTOR
2
1.2V
V
CAL _ ADC _ 20VREF _ FACTOR
2
2.0V
V
CAL _ ADC _ 25VREF _ FACTOR
2
2.5V
+
+
+
=
´
=
´
=
´
Device Descriptor Table
68
SLAU367P – October 2012 – Revised April 2020
Copyright © 2012–2020, Texas Instruments Incorporated
System Resets, Interrupts, and Operating Modes, System Control Module
(SYS)
1.14.3 Calibration Values
The TLV structure contains calibration values that can be used to improve the measurement capability of
various functions. The calibration values available on a given device are shown in the TLV structure of the
device-specific data sheet.
1.14.3.1 REF Calibration
shows the REF calibration tags.
Table 1-6. REF Calibration Tags
REF
Calibration
TAG
12h
Length
06h
Low Byte
CAL_ADC_12VREF_FACTOR
High Byte
Low Byte
CAL_ADC_20VREF_FACTOR
High Byte
Low Byte
CAL_ADC_25VREF_FACTOR
High Byte
The calibration data for the REF module consists of three words, one word for each reference voltage
available (1.2 V, 2.0 V, and 2.5 V). The reference voltages are measured at room temperature. The
measured values are normalized by 1.2 V, 2.0 V, or 2.5 V before being stored into the TLV structure, as
shown in
(2)
In this way, a conversion result is corrected by multiplying it with the CAL_12VREF_FACTOR (or
CAL_20VREF_FACTOR, CAL_25VREF_FACTOR) and dividing the result by 2
15
as shown in
for each of the respective reference voltages:
(3)
In the following example, the integrated 1.2-V reference voltage is used during a conversion.
•
Conversion result: 0x0100 = 256 decimal
•
Reference voltage calibration factor (CAL_12VREF_FACTOR) : 0x7BBB
The following steps show how the ADC conversion result can be corrected:
•
Multiply the conversion result by 2 (this step simplifies the final division): 0x0100 x 0x0002 = 0x0200
•
Multiply the result by CAL_12VREF_FACTOR: 0x200 x 0x7FEE = 0x00F7_7600
•
Divide the result by 2
16
: 0x00F7_7600 / 0x0001_0000 = 0x0000_00F7 = 247 decimal
1.14.3.2 ADC Offset and Gain Calibration
shows the ADC calibration tags.