Down translation means level-shifting from a higher voltage to a lower voltage, or in this case, from side B to side A. Nexperia recommends the customer always connects the B-side to the higher voltage domain, as the B-side must supply the drive current. For the B-side to drive a low-level signal, an external device such as an NMOS transistor pulls down the B-side voltage and the pass transistor conducts. This causes the A-side voltage to be pulled low as well. For the B-side to drive a high-level signal, the pass transistor is turned off. This causes the A-side voltage to be pulled high due its external pull resistor.