Description:
PVD and USB wakeup, which are internally linked to EXTI line16 and EXTI line 18, respectively, cannot be used as event sources for the Cortex-M3 core. As a consequence, these signals cannot be used to exti the Sleep or the Stop mode.(exti WFE)
Workaround:
Use interrupt sources and the WFI instruction if the application must be woken up from the Sleep or the Stop mode by PVD or USB wakeup.