As with many amplifiers, the PGA has an absolute input voltage range requirement that cannot be exceeded. The maximum and minimum absolute input voltages are limited by the voltage swing capability of the PGA output. The specified minimum and maximum absolute input voltages (VAINP and VAINN) depend on the PGA gain, the maximum differential input voltage (VINMAX), and the tolerance of the analog power-supply voltages (AVDD and AVSS). Use the maximum voltage expected in the application for VINMAX. The absolute positive and negative input voltages must be within the specified range, as shown in Equation 5:
As mentioned in the previous section, PGA gain settings of 64 and 128 are scaled in the digital domain and are not implemented with the amplifier. When using the PGA in gains of 64 and 128, set the gain in Equation 5 to 32 to calculate the absolute input voltage range.
The relationship between the PGA input to the PGA output is shown graphically in Figure 51. The PGA output voltages (VOUTP, VOUTN) depend on the PGA gain and the input voltage magnitudes. For linear operation, the PGA output voltages must not exceed AVDD – 0.15 V or AVSS + 0.15 V. Note that the diagram depicts a positive differential input voltage that results in a positive differential output voltage.