I'm designing a custom Blackfin board and basing it on the BF 533 EZ-KIT. I need to put the system to sleep and have absolutely minimum quiescent current draw for a 1:10 ratio (i.e. awake and processing for 10% of the time). On the BF 533 EZ-KIT an ADP1864 switched mode regulator is used to generate a 3.3 V rail for memory, UARTS etc. I intend to replace this component with something similar but with a shutdown pin so I can switch off this rail during sleep periods (the processor will wake with an RTC interrupt). A linear regulator is used in the EZ_KIT to generate a 3.3 V supply for the processors VDDEXT rail and as a source for a switched mode 1.2 V supply for VDDINT. Why was a linear regulator used for the processors VDDEXT rail rather than a more efficient switched mode unit? Would it be preferred to utilise a switched mode 3.3 supply for VDDINT in battery powered applications?