TMS570LS3137

The data sheet says that ADREFHI should be less than or equal to VCCAD. If it were necessary to use two separate regulators to power VCCAD at 5.1V and ADREFHI at 5.0V would it be acceptable to have the 5.0V rail power up faster than the 5.1V rail? Would that damage the ADC module?

I believe you would be well within the 5.1 Absolute Maximum Ratings confines in this case so I'd say no damage. Proper operation during the ramp - no but you probably wouldn't expect that anyway.

Also, having to use 2 vregs is a bit unusual.

Yes, I agree. The design uses a REF5050 for ADREFHI so there is a very accurate and stable reference, and a different regulator to supply 5.1V to VCCAD and another circuit. The REF5050 can only source 10mA, but both ADC modules and references in the TMS570 require a maximum current of 36mA. I am trying to see if the tolerances can be loosened a bit to allow just one regulator for both.