In the AM1808 Silicon Errata (SPRZ313B), Advisory 2.0.18, the following statement is made:
"The 3.3V DVDD3318_x supplies must not be driven to 0V during zones A – E or high current capable of damaging the device may occur. The 3.3V DVDD3318_x supplies should not be driven during this time."
This conflicts with the AM1808 datasheet (SPRS653A), section 6.3.1:
"There is no specific required voltage ramp rate for any of the supplies as long as the LVCMOS supplies operated at 3.3V (DVDD3318_A, DVDD3318_B, or DVDD3318_C) never exceed the STATIC 1.8V supplies by more than 2 volts."
I don't see any way to guarantee that the 3.3V supply will be less than 2V above the 1.8V supply, other than to shunt it to ground when the 1.8V supply is below a certain value. Of course, one could turn off the shunt when the 3.3V supply is below 2.0V, but that would be a more complex circuit.
Any recommendations?