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2014-07-02 - Gecko Family - d0001_Rev1.30
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Figure 25.4. ADC RC Input Filter Configuration
ADC
Input
R
C
25.3.4.2 Temperature Measurement
The ADC includes an internal temperature sensor. This sensor is characterized during production and the
temperature readout from the ADC at production temperature, ADC0_TEMP_0_READ_1V25, is given
in the Device Information (DI) page. The production temperature, CAL_TEMP_0, is also given in this
page. The temperature gradient, TGRAD_ADCTH (mV/degree Celsius), for the sensor is found in the
datasheet for the devices. By selecting 1.25 V internal reference and measuring the internal temperature
sensor with 12 bit resolution, the temperature can be calculated according to the following formula:
ADC Temperature Measurement
T
CELSIUS
=CAL_TEMP_0-(ADC0_TEMP_0_READ_1V25-
ADC_result)×Vref/(4096×TGRAD_ADCTH)
(25.2)
Note
The minimum acquisition time for the temperature reference is found in the electrical
characteristics for the device.
25.3.5 Reference Selection
The reference voltage can be selected from these sources:
• 1.25 V internal bandgap.
• 2.5 V internal bandgap.
• V
DD
.
• 5 V internal differential bandgap.
• External single ended input from Ch. 6.
• Differential input, 2x(Ch. 6 - Ch. 7).
• Unbuffered 2xV
DD
.
• The 2.5 V reference needs a supply voltage higher than 2.5 V.
• The differential 5 V reference needs a supply voltage higher than 2.75 V.
Since the 2xV
DD
differential reference is unbuffered, it is directly connected to the ADC supply voltage
and more susceptible to supply noise. The V
DD
reference is buffered both in single ended and differential
mode.
If a differential reference with a larger range than the supply voltage is combined with single ended
measurements, for instance the 5 V internal reference, the full ADC range will not be available because
the maximum input voltage is limited by the maximum electrical ratings.
Note
Single ended measurements with the external differential reference are not supported.
25.3.6 Programming of Bias Current
The bias current of the bandgap reference and the ADC comparator can be scaled by the BIASPROG,
HALFBIAS and COMPBIAS bit fields of the ADCn_BIASPROG register. The BIASPROG and HALFBIAS
Summary of Contents for EFM32G
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