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Alternate 1.2V power source question

Question asked by John Fielden on Sep 21, 2013
Latest reply on Nov 25, 2013 by John Fielden



I have a different suggestion for a 1.2V supply for the Vybrid.  In my system, I have a 1.8V rail that I use to LDO down to 1.5V for the DDR3.  I would like to use the 1.8V for the collector voltage, but the 1.8V supply and the 3.3V supply are separate switching supplies.   It seems to me that the important thing for the BJT is that the collector voltage is present when the 3.3V comes up.  If so, can I use the power good output from the 1.8V supply to turn on the 3.3V supply?


In practice, an external entity will turn on the Vybrid by turning on the 1.8V supply, which in then turns on the 3.3V supply, which then power up the BCTRL circuitry and provides 1.2V.  When we shut down, the 1.8V will fall first, then the 3.3V.  I read somewhere that the core should call before the 3.3V, which seems odd to me, but would occur using this scenario.


See the block diagram below.