Regarding OPA657 suffixes, please refer to below note or page 19 & 29 of the datasheet for further detail.
U: SOIC
N: SOT-23-5
B: High-grade (precision) version
For the best DC precision, a high-grade version (OPA657UB or OPA657NB) screens the key DC parameters to an even tighter limit. Both standard- and high-grade versions take advantage of a new final test technique to 100% test input offset voltage drift over temperature.
This discussion uses the high-grade typical and min/max Electrical Characteristics: VS = ±5 V for illustration; however, an identical analysis applies to the standard-grade version. The total output DC offset voltage in any configuration and temperature is the combination of a number of possible error terms.
In a JFET part such as the OPA657, the input bias current terms are typically quite low but are unmatched. Using bias-current cancellation techniques, more typical in bipolar input amplifiers, does not improve output DC offset errors. Errors due to the input bias current only become dominant at elevated temperatures.
