i've made further test
it seems that with a sensitivity of 0.034/2 it works from 4A to 12A quite well.
0.034 seems ok, because my supply is 4.7V, sensitivity should be 0.03824 +- 5mV (Electrical offset voltage from datasheet)
but i've to use half of it.
p.s checked also my multimeter and it has no problem.
have you any suggestion, or anyone here that can test my code on other chip?
tks!