Texas Instruments ADS1x48EVM, User Manual, Page: 17 / 48

3.5.3 Connecting an RTD to J6 on the ADS1x48EVM
The RTD input connections on J6 are J6:3, J6:4, and J6:5, which correspond to the RTD_A, RTD_B, and
RTD_C nets, respectively. Additionally, terminal block J6 provides a pair of differential reference inputs, REFP1
and REFN1, which correspond to inputs J6:1 and J6:2, respectively. The RTD_A, RTD_B and REFP1, REFN1
input pairs have a differential filter with a cutoff frequency of 1.93 kHz. Additionally, each of these inputs has
a common-mode filter with a cutoff frequency of 38.63 kHz.
Figure 3-12 shows the RTD input structure on the
ADS1x48EVM, and Table 3-4 describes the mapping between the terminal block connections, schematic net
names, and the analog pins on the ADS1x48. Some nets may connect to multiple analog pins on the ADS1x48.
REFP1
REFN1
REFP1
REFN1
4.12k
R20
4.12k
R28
0.01uF
C18
1000pF
C21
1000pF
C11
AIN3
AIN2
680
R18
IEXC2
RTD_A
RTD_B
RTD_A
RTD_B
680
R29
IEXC1
RTD_C
AIN1
AIN0
RTD_C
0.01uF
C5 1000pF
C2
1000pF
C6
4.12k
R10
4.12k
R12
4.02k
R11
GND
GND
GND
1
2
3
4
5
6
J6
GND
GND
JP3
JP4
JP5
JP6
Figure 3-12. RTD Input Structure on the ADS1x48EVM
Table 3-4. ADS1x48EVM Terminal Block (J6) to ADC Connections
Connector Net Name ADS1x48 Input Connection Description
J6:1 REFP1
REFP1 External reference input (positive)
AIN1 Analog input 1
J6:2 REFN1
REFN1 External reference input (negative)
AIN0 Analog input 0
J6:3 RTD_A
AIN2 Analog input 2
IEXC2 Excitation current source #2
J6:4 RTD_B
AIN3 Analog input 3
IEXC1 Excitation current source #1
J6:5 RTD_C IEXC1 Excitation current source #1
J6:6 GND n/a Analog ground
In Figure 3-12 , resistor R11 is the reference resistor (R
REF
) that is placed in series with the RTD and connected
to the ADS1x48 external reference inputs, as described in Table 3-4 . An excitation current supplied by one of
the two IDACs integrated into the ADS1x48 flows through R
REF
and the RTD, creating a ratiometric relationship
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SBAU378A – SEPTEMBER 2021 – REVISED JANUARY 2022
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ADS1x48EVM Evaluation Module 17
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