I am using the ADA4891 op amp in a single 5V supply configuration as an ADC preamp. The datasheet indicates rail to rail performance within 50mV of each rail. I have tested a single ADA4891 unit on a breadboard and have confirmed the datasheet. However, the SPICE model shows complete clipping at about 600mV below the 5V rail. Why does the SPICE model not agree with the datasheet and the single unit I have tested. Thanks.