I am using 16F877A for a ADC conversion from a temprature sensor LM35.
If I use VDD as reference, I get 5/1024 = 4.8mv appx resolution. I am thinking of using Vref as a reference and I would like to know how much minimum voltage can I put on Vref pin? I am thinking if I am able to put 1.1 volt then I get appx 1mV resolution. Am I thinking around the right lines or something is wrong with my planning?

I would also like to know where to get to this info from the datasheet if possible. Thanks