Issues in relation to which referendums are mandatory at the national level

Botswana
Constitution (1966)
http://aceproject.org/regions-en/eisa/BW/Constitution%20of%20Botswana%201966.pdf
Constitution (1966),
89. Alteration of Constitution.
In so far as it alters any of the provisions mentioned in subsection (3)(b) of this section no Bill shall be presented to the President for his assent unless after its passage by the Assembly it has been submitted to the electors qualified to vote in the election of the Elected Members of the National Assembly, and, on a vote taken in such manner as Parliament may prescribe, the majority of the electors voting have approved the Bill.