Lets say you're doing a pull/push or upper/lower split
To train back,all you need is
FOR WIDTH
chin ups for 3 sets
FOR THICKNESS
any form of rows for 3 sets of 6-8
FOR POWER
HEAVY rack pulls for 3 sets of 4-5
The back is a very large body part
The chins will take care of predominatly the lats,the rows will work mostly the mid back and the rack pulls will fry the traps and lower back.
That's not to say,for example,chins only work the lats,they also,to a lesser but still very significant extent,other part of the back especially midback and traps.Same goes for the other 2 movements.
Good luck!