The output of the 3.3-V LDO can be used to power the entire MSP430 device, sourcing the DVCC rail. If this is desired, the VUSB and DVCC should be connected externally. Power from the 3.3-V LDO is sourced into DVCC (see Figure 42-4).
With this connection made, the MSP430 allows for autonomous power up of the device when VBUS rises above VLAUNCH.LAUNCHvoltage is present on VCORE – meaning the device is unpowered (or, in LPMx.5 mode) – then both the 3.3-V and 1.8-V LDOs automatically turn on when VBUS rises above VLAUNCH.LAUNCHhat if DVCC is being driven from VUSB in this manner, and if power is available from VUSB, attemptiattempte the device into LPMx.5 results in the device immediately re-powering. This is because it re-creates the conditions of the autonomous feature described above (no VCORE but power available on VBUS). The resulting drop of VCOREinould causes the system to immediately power up again. When DVCC is being powered from VUSB, it is up to the user to ensure that the total current being drawn from VBUS stays below IDET.