J4 Thermocouple Input - Texas Instruments ADS126 EVM-PDK Series User Manual

ADS126xEVM Hardware
2.6.3 Thermocouple Input
Terminal block J4, shown in
block is surrounded by a cutout ground plane polygon to provide partial thermal isolation for thermocouple
inputs. Thermocouples can be biased either by enabling the VBIAS level shifter and shorting jumper JP5,
or by enabling the 1-MΩ pull-up and pull-down resistors inside the ADS126x.
Cold junction compensation of the thermocouple is implemented by the thermistor on RT1 to measure the
cold junction temperature. Install 0-Ω resistors on R22 and R24 (0603 surface-mount pads) to connect
RT1 to inputs AIN6 and AIN7 on the ADS126x. R23 is in parallel with RT1 for linearization of the
thermistor resistance versus temperature transfer function.
NOTE: Do not use the IN6 and IN7 inputs on terminal block J2 if components are soldered to R22
or R24. Interaction between components causes measurement error.
2.6.4 X2Y Capacitor Footprints
®
Capacitors C2, C8, C17, C24, and C35 are unpopulated footprints reserved for 0603 X2Y capacitors. X2Y
capacitors can replace the multiple capacitors (C1, C3, and C4 for example) required for common-mode
and differential filtering. In addition to the board space saved by using X2Y, these capacitors have lower
ESL and excellent common-mode capacitor matching.
16
ADS126xEVM-PDK
Figure 12, connects to inputs AIN8 and AIN9 on the ADS126x. The terminal
Figure 12. J4 Thermocouple Input
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SBAU206 – April 2015
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