Texas Instruments ADS1285EVM-PDK, User Manual, Page: 6 / 40

3 EVM Analog Interface
The ADS1285EVM-PDK is designed for easy interfacing with analog sources. This section details the front-end
circuit, including jumper configuration for different input test signals and board connectors for signal sources.
3.1 ADC Analog Input Signal Path
Analog inputs to the EVM can be connected to either terminal block associated with each ADC channel. The
screw terminal blocks (J12, and J13) can interface directly with the leads of an external sensor input.
Figure
3-1 depicts the signal chain used for the two input channels on the EVM and Table 3-1 lists the supported input
options.
An input must not be applied such that the voltage on the input pins of the ADS1285 exceeds the absolute
maximum ratings. For more details, see the
ADS1285 data sheet .
R45 and R46 provide common-mode voltage paths for the channel 1 inputs. See Section 5 for more information.
In addition, R43 and C29 (in combination with R47 and C31) provide the common-mode, low-pass filters for
the positive and negative inputs, respectively. Furthermore, R44 and R40 in combination with C30 provides the
differential low-pass filter used in antialiasing. The series impedance is kept relatively low to maintain adequate
total harmonic distortion (THD) performance. Similar differential and common-mode, low-pass filter footprints are
present on all inputs.
Specifically for channel 2, the default configuration is set up to use the DAC1282 on the input. As a result,
the common-mode filters for this configuration are not populated, and R50, R54, and C33 are optimized for
the output of the DAC. There are two options for connecting the DAC to the channel 2 of the ADS1285: using
the direct output of the DAC1282 or the integrated switches of the DAC1282. By default, the direct output of
the DAC1282 is used by populating R55 and R59. As a result, using the integrated switches is achieved by
depopulating R55 and R59, populating R56 and R58, and configuring the DAC using the GUI as described in
Section 6 . For best THD performance (approximately a 1-dB difference), use the direct output. For maximum
flexibility, use the integrated switches.
EVM Analog Interface www.ti.com
6 ADS1285EVM-PDK Evaluation Module SBAU394A – APRIL 2022 – REVISED SEPTEMBER 2022
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