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I currently placed two MCU supply voltages on the DIMM connector: +5V which is connected to the USB 5V, and +3V3, which is connected to the output of the LDO inside the MSP430 (this LDO is fed by the +5V). I wanted to have the backplane supply 5V only if it used the USB connection and supply 3.3V otherwise. But there should be a different way to detect the presence of the USB host. So any concerns about removing the +3V3 signal from the DIMM?