I am working on a project that mandates the use of a particular Arduino motor driver shield, which makes use of an L298 dual H-bridge (datasheet here)

I need to perform some power calculations in order to size up my power supply, and ensure that I keep the driver's self-heating manageable. If my understanding is correct, in DC operation, an H-bridge will dissipate \$P = I^2(RDS_{on(H)} + RDS_{on(L)})\$

Unfortunately, the datasheet doesn't mention \$RDS_{on}\$. Is there some other way to calculate the power dissipated in a H-bridge that I am missing?