AD1877: Calculation of the LSB value

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Question How to calculate the LSB value in microvolts for an AD 1877JR? 
 There is some confusion with the 1.333 factor given in the data sheet 
 AD1877.pdf_page2_rev0. What is the applicable value to 2^15 Full Scale?
 Vref or Vref x 1.333 ? Answer The answer to your question is to be found on page 8 of the datasheet in the 
 section APPLICATIONS ISSUES:Analog Input voltage swing. 
 
 Nominally the analog input span is 3.1V, that is, Vref+/- 1.55V. Therefore 
 there is a little confusion when Vinpp is given as Vref x 1.333 which is 3.0V 
 (taking Vref at it's nominal value of 2.25V)
 
 However, on page 8 it is explained that the analog input span actually scales 
 with the reference voltage.
 Since the reference voltage is fairly loosely specified in terms of absolute 
 accuracy (+300mV / - 200mV) there is also a fairly large variation in the input 
 span. The formula on page 8 shows that the analog input span is in fact 
 proportional to the reference voltage. If you rearange the formula you get
 
 Yvolts = Xvolts x 1.378 
 
 where:
 Yvolts is the maximum swing without clipping
 Xvolts is the measured reference and 1.378 is the ration between nominal 
 voltage swing and nominal reference voltage
 
 So, the 1.333 factor given on page 2 is simply being cautious, by stating a 
 limit for the input signal which will ensure no clipping takes place. In fact, 
 the "real" number is 1.378, so to calculate the lsb size
 
 1lsb = Vref x 1.378 /2^16 =47.3uV for a nominal reference of 2.25V. The lsb 
 size will change depending on the actual value of the reference for the 
 particular device in question.

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AD1877: FAQ