I am looking into two different development boards which uses TLC2543 and ADS7870 for A to D conversion. From comparing both IC's I have found out that the resolution of both is 12 bit. However, development board manufacturer mention ADS7870 being 11 bit. The data sheet of development board using ADS7870 for A to D conversion say 11 bits are used for value and 1 bit for polarity. Is that true? Is it the case with all 12 bits A to D converters ?
The difference is because the TLC2543 is a single ended input ADC, while the ADS7870 is a differential input ADC. When using a single ended input the input will always be between the common pin (GND) and the Vref voltage. Using a differential input the input (using the names of A and B for the inputs) of A will sometimes be more positive than input B and sometimes input B will be more positive than input A. In that case the input will need to be between -Vref and +Vref. Please compare Figure 16 in the TLC2543 datasheet and Figure 13 in the ADS7870 datasheet.
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