Texas Instruments ADS1263EVM-PDK User Manual page 7

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3.1.2.2), and RTDs (see Section
terminals J3-J6 on the ADS1263EVM, as per
3.1.2.1 Connecting a Thermocouple to J4 on the ADS1263EVM
Measure an external thermocouple by connecting the sensor directly to the J4:1 and J4:2 inputs on the J4
terminal block. The differential filter for this differential input pair has a cutoff frequency of 50 kHz. Additionally,
each input has a common-mode filter with a cutoff frequency of 497.36 kHz. J4 is connected through the filter
resistors to analog inputs AIN8 and AIN9 on the ADS1263.
schematic with J4 and the thermocouple input structure.
J4
1
2
J5
1
2
Although thermocouples are self-powered, these components must be biased to avoid floating beyond the
input range of the PGA integrated into the ADC. Thermocouples are typically biased to AVDD / 2 because
AVDD / 2 is also the middle of the PGA common-mode range. Designing a bias circuit at this voltage therefore
enables the largest gain for any given thermocouple voltage. The ADS1263EVM offers multiple ways to bias the
thermocouple so the output voltage can be successfully read by the ADS1263.
The first method uses pullup and pulldown resistors to center the thermocouple output voltage at AVDD / 2.
Figure 3-2 shows that these resistors are designated R3 and R4 on the ADS1263EVM, but are not installed
by default. Therefore, 1-MΩ to 10-MΩ resistors must be installed at R3 and R4 to use the pullup and pulldown
resistor biasing scheme. One added benefit of using pullup and pulldown resistors is that these resistors
enable continuous sensor break detection. If one of the thermocouple wires breaks, AIN8 is pulled up to AVDD
and AIN9 is pulled to GND. These conditions cause the ADC to measure a full-scale input that is easily
distinguishable from the normal, low-level thermocouple output voltage.
The second thermocouple biasing method that is supported by the ADS1263EVM uses the ADS1263 internal
reference from REFOUT (J5:2).
input (J4:2) and REFOUT output (J5:2) to bias the thermocouple input voltage to 2.5-V. One challenge with the
configuration in Figure 3-3
wire-break detection using a separate diagnostic measurement or by installing pullup resistor R3.
SBAU206B – APRIL 2015 – REVISED MAY 2023
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3.1.2.4). Connect these sensors as well as other similar devices across
Figure
AVDD
R3
DNP
10M
AIN8
AIN9
R4
DNP
10M
GND
AINCOM
R21 1.00k AINCOM
C21
150pF
AINCOM
REFOUT
GND
REFOUT
REFOUT
Figure 3-2. ADS1263EVM Thermocouple Input Structure
Figure 3-3 illustrates how to connect an external jumper between the AIN9
is that this option does not offer continuous wire-break detection. Instead, perform
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3-1.
Figure 3-2 shows the portion of the ADS1263EVM
R13
1.00k
C12
150pF
GND
C13
150pF
R14
1.00k
Analog Interface
TP22
A8
C19
1600pF
TP2
A9
ADS1263EVM-PDK Evaluation Module 7