Can PDB and PDB2 be tied together without loss in amp-to-amp isolation? Are these truly digital inputs? I want to run these enable pins off of the 5V I'm using for powering the chip. I will use a voltage divider with a 10K from 5V to these pins and a 15K from these pins to ground. This should give me a 3V input for these pins. As an alternative, the data sheet says they are internally pulled up to 2.8V so can I just leave these open to enable the amps? What does ADI recommend?
Yes, if you leave PDB and PDB2 unconnected, it will be internally pulled up and thus enable the amps. Any trace crossing between the amps may result in coupling, so proper layout techniques should be used to mitigate the adverse affects if crossing is unavoidable. Luckily, it's not necessary in this particular case.