The current and voltage curve of latch-up is shown in the left figure. The unconducted latch-up will be in a state where the current is almost zero. If the latch-up is triggered to conduct, then it will enter a huge current state where the V_DD and the curve intersect in the upper part of the curve. When the energy of this huge current is large enough, it may burn the internal components of the chip seriously. That would form the latch-up damage phenomenon as shown in the right image.