The design is intended to be used with a Precision Host Interface (PHI) board, allowing for easy connection with the ADS127L21 GUI. The PHI board is a peripheral used to interface with GUIs for several of Texas Instrument's delta-sigma ADCs. This board cannot be ordered individually, however, the board is provided with the purchase of ADS127L11EVM-PDK or ADS127L21EVM-PDK. The ADC power and clocking are sourced from the PHI controller by default. The reference design additionally contains an on-board, high precision 4.096V series reference to maximize the ADC's dynamic range. However, the user can choose to use an external reference, clock, and power supply, depending on the system specifications. Regardless of how the ADC is powered, the PGA855 must be powered externally. Additionally, there is a header on the board which allows access to the digital lines from the ADC if the PHI controller board is not used.

The ADC has two input ranges: 1x and 2x, where the 1x range is defined by VIN = ± VREF and the 2x range is defined by VIN = ± 2 × VREF. The 2x input range doubles the available range when using a reference voltage of 2.5V or less. The 2x input range typically improves SNR by 1dB when using a 2.5V reference, but also requires driving the inputs to the 5V supply rails to achieve full dynamic range. The best available dynamic range (4dB improvement, typical) is through the use a 4.096V or 5V reference voltage (program the ADC to the high-reference range mode).

This design has a wide input range, due to the PGA855 gain settings. The maximum input signal to the board depends on the PGA855 power supplies, the PGA gain setting, and the input range selection on the ADC. The maximum recommended power supply for the PGA855 is 36V unipolar or ± 18V bipolar. For example, with a 4.096V reference, the system full-scale range varies from ± 0.256V (16V/V gain) to ± 32.768V (1/8V/V gain), when the PGA855 is powered from ± 18V supplies.