There is no restriction on the power-up sequence. In case the VDDOUT is applied first, TI recommends grounding VDD. In case the VDDOUT is powered while VDD is floating, there is a risk of high current flowing on the VDDOUT.
The device has a power-up control that is connected to the 1.8-V supply. This keeps the whole device disabled until the 1.8-V supply reaches a sufficient voltage level. Then the device switches on all internal components, including the outputs. If there is a 3.3-V VDDOUT available before the 1.8-V, the outputs stay disabled until the 1.8-V supply reaches a certain level.