Texas Instruments MSP430FR57 Series, User Manual, Page: 46 / 578

15
2
1
_ 15 _ ) ( ) (
´ ´ =
FACTOR VREF ADC CAL raw ADC corrected ADC
15
2
1
_ 20 _ ) ( ) (
´ ´ =
FACTOR VREF ADC CAL raw ADC corrected ADC
15
2
1
_ 25 _ ) ( ) (
´ ´ =
FACTOR VREF ADC CAL raw ADC corrected ADC
15
2
5 . 1
_ 15 _ _
´ =
+
V
V
FACTOR VREF ADC CAL
REF
15
2
0 . 2
_ 20 _ _
´ =
+
V
V
FACTOR VREF ADC CAL
REF
15
2
5 . 2
_ 25 _ _
´ =
+
V
V
FA C TO R V R E F A D C C A L
R E F
Device Descriptor Table
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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
Table 1-6 shows the REF calibration tags.
Table 1-6. REF Calibration Tags
REF TAG 12h
Calibration
Length 06h
Low Byte
CAL_ADC_15VREF_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 (1.5 V, 2.0 V, and 2.5 V). The reference voltages are measured at room temperature. The
measured values are normalized by 1.5 V, 2.0 V, or 2.5 V before being stored into the TLV structure, as
shown in
Equation 2 :
(2)
In this way, a conversion result is corrected by multiplying it with the CAL_15VREF_FACTOR (or
CAL_20VREF_FACTOR, CAL_25VREF_FACTOR) and dividing the result by 2
15
as shown in Equation 3
for each of the respective reference voltages:
(3)
In the following example, the integrated 1.5-V reference voltage is used during a conversion.
• Conversion result: 0x0100 = 256 decimal
• Reference voltage calibration factor (CAL_15VREF_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_15VREF_FACTOR: 0x200 x 0x7FEE = 0x00F7_7600
• Divide the result by 2
16
: 0x00F7_7600 / 0x0001_0000 = 0x0000_00F7 = 247 decimal
46 System Resets, Interrupts, and Operating Modes, System Control Module SLAU272C – May 2011 – Revised November 2013
(SYS)
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