Does PGA281 analog power supply VSP/VSN has revers protection inside device?
withe Gain 1 (or lower), what is the minimum input signal level? I found the output is not right level when input is 15mV Diff.
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The PGA281 does not have internal reverse supply protection diodes.
It is always good practice to add external protection TVS diodes on each (VSN/VSP) supply to protect the device for over-voltage conditions or reverse supply conditions. Also observe the maximum VSON/VSOP and DVDD supply rating since there is no internal protection; and may need to add external TVS diode protection to these supplies as well if there is risk that the device will be exposed to an over-voltage or reverse voltage conditions on those supplies as well.
Please carefully review the "Absolute Maximum Ratings" specifications on page (2), the "Power Supply Range limits" on the Electrical Characteristics table on page 5, and the "Power Supply" detailed discussion on page 20 of the PGA281 datasheet.
There is a generic TI Precision labs tutorial section that discuss the selection of the optimal TVS diodes for a given a supply/device specification that you may find useful:
Regarding the input voltage range:
There is no minimum differential voltage specification; the differential voltage can be positive or negative.
The input referred offset error of the PGA281 is small, in the order of +/-50uV typical (Gain=1), +/-255uV maximum (Gain=1); well below the 15mV differential.
However, please notice that the positive (INP) and negative input (INN) absolute voltage must remain inside the allowed common-mode range, where the absolute input voltage at the INP1 and INN1 inputs must be at least 2.5V from the positive (VSP) and negative supply rail (VSN); or in other words, the absolute voltage input range has to be within (VSN)+2.5V and (VSP)-2.5V on both positive and negative inputs.
Thank you and Regards,