Teensy 3.2 AREF(EXTERNAL) and analogRead()

[alexsh1]

Hello all,

I am using the external voltage reference 2.048V with Teensy 3.2
Then I am feeding voltage I am measuring (0-5V) via a voltage divider (0.5 ratio) to an analogue pin.
However, I can only read voltages via ADC up to 4.09V (I think it is 2 x AREF). Above that the value of analogRead() does not change.
Why is it the case? Do I need 2.5V external voltage reference fed into AREF pin?

Thanks for your help.
Regards
Alex