The ADS1258EVM allows for up to 16 single-ended inputs or eight differential inputs, as well as combinations of single-ended and differential inputs. As shown in Figure 3-1, connect analog input signals to terminal blocks J1 and J2 on the EVM.

Figure 3-1 ADS1258EVM Analog Input Channels and Filtering

Each analog input signal passes through a set of low-pass filters to prevent aliasing. The differential filters have a 3-dB cutoff of 168.5 kHz, resulting in 33.49 dB of attenuation at the 8-MHz modulator frequency. As an example, Figure 3-1 shows that capacitor C13 and resistors R22 and R26 create the differential filter between analog inputs AIN0 and AIN1. The common-mode filters have a 3-dB cutoff of 3.37 MHz. As an example, Figure 3-1 shows that capacitor C11 and resistor R22 create the common-mode filter for analog input AIN0. Precision 5% C0G or NPO-type capacitors and 0.1% resistors are used in the analog signal chain to reduce measurement error.

Use adjacent input pins when measuring differential input signals to benefit from differential filtering and to achieve best performance. For example, AIN0 and AIN1 are set up for differential signaling because C13 connects these two inputs. Conversely, do not use AIN1 and AIN2 as a differential pair because there is no capacitor connecting these two inputs.