ADS1220EVM Hardware Details
5.2.3
RTD Terminal Block J2
J2 is a four-position screw terminal block that can accept wire sizes AWG 28-16. The main purpose for J2
is to provide a connection for measuring a resistance temperature device (RTD). A two-, three-, or four-
wire RTD can be connected to J2. Measurement channels are AIN0 and AIN1. Current excitation is
directly possible from AIN0, AIN1, and AIN2. For three-wire RTDs, any combination of two excitation
sources can be used.
One problem with using a three-wire RTD is in regards to driving current through analog input filtering.
This problem can be avoided by installing resistor R30, which allows AIN3 to be used as a second current
source. Placing a 0-
Ω
resistor at R30 creates a direct connection between AIN3 and J2.3 (AIN1).
lists pin descriptions.
RTD measurement is best as a ratiometric measurement. Excitation current establishes a reference
voltage at the dedicated reference REP0/REFN0. 'Establishing the reference voltage requires that a bias
resistor be installed at R3. R3 should be a precision, low-drift resistor. The value chosen depends on the
RTD value and excitation current, as well as maintaining IDAC voltage compliance for the ADS1220. For a
complete current path, one side of R3 (REFN0 side) must connect to AGND. The easiest way to
accomplish this connection is to place a shorting jumper from J4.9 to J4.7.
Table 7. J2: RTD Terminal Block Connector
Description
Signal
Pin Number
Analog input, negative (IN–)
AIN1
J2.3
(1)
Analog input, positive (IN+)
AIN0
J2.2
Reference bias resistor connection
(2)
REFP0
J2.4
RTD current excitation
(3)
AIN2
J2.1
(4)
(1)
When using a three-wire RTD, AIN3 can be used as a current source by installing a 0-
Ω
resistor at R30.
(2)
Bias resistor R3 must be installed. To complete the current path, REFN0 must also be connected to ground.
(3)
Direct connection to three- and four-wire RTDs. A two-wire RTD requires a jumper between J2.1 and J2.2 as well as between
J2.3 and J2.4. Three-wire RTDs require an additional excitation current.
(4)
Pin 1 is at the top left-hand corner of the EVM, located opposite from the reference designator.
5.2.4
Thermocouple Connector, J3
Provision for a miniature thermocouple connector is provided on the EVM. The socket connector footprint
accommodates the Omega
®
PCC-SMP-style connector at J3. The J3 connector should be installed on the
bottom-side of the EVM. The J3 terminals connect to AIN1 and AIN2 of the ADS1220. Biasing resistors R1
and R2 can be installed to place the thermocouple into the correct common-mode input range of the
ADS1220.
A cold-junction area is provided for compensation (CJC) and the ADS1220 temperature sensor can be
used to measure the temperature of the cold junction. Provision for a RTD chip temperature-sensing
device is located at R31. An example of what can be used at R31 is the Vishay
®
Beyschlag
PTS120601B100RP100. When using a RTD at R31, excitation current is provided from AIN3. For a
complete current path, AIN3 must connect to R31. This connection can be accomplished by placing a
jumper wire at J4.2 to J4.8 of connector J4. Similar jumper options are also available at connectors J1 and
J6.
5.2.5
Analog Input Filtering Options
The analog input connectors directly connect to the ADS1220 inputs using 0-
Ω
resistors by default. Filters,
such as antialiasing or electromagnetic interference and radio frequency interference (EMI/RFI), can be
installed using the resistor and capacitor pads available at the analog side of the ADS1220. These pads
are found on both the top- and bottom-side of the EVM. Device pads are available to create filter
combinations for both differential and common-mode filters for many different input configurations. Filtering
combinations are also included for filtering the external reference inputs.
12
ADS1x20EVM
SBAU203 – July 2013
Copyright © 2013, Texas Instruments Incorporated