Quiescent or operating?
With or without load?
At its minimum or maximum voltage?
I will be looking at TI's datasheet revision E when I mention figures.
1) I would start by reading the datasheet's supply current vs. voltage and temperature. Figure 1. Multiply by supply voltage.
2) Then take all the output load currents (which include the pullup resistors, use ohm's law), and multiply it by the output saturation voltage, figure 3.
3) The losses dissipated by the actual switching....that will be a tough one as it is not specified. But as a ballpark value, if you are switching slowly, below 1 KHz, leave the sum of 1 and 2 as is. Add 10% for each additional decade of switching frequency. Again, this is only a ballpark value.