Re: square wave aplitude
Sorry I missed the part about the analogue IC.
A voltage divider will work for such a low frequency if there is plenty of current available.
It would be necessary to check that the input resistance of the pin and take it into consideration when picking the values for the divider.
An o/c buffer will provide a more stable and guaranteed (high)voltage level, which will not be sensitive to changes in loading at any input pin. The buffer will however increase the total power consuption of the system, but not by much.