Plunking 0304 into the marking lookup on TI's website hits on the TPS40304, whose package completely matches what you describe, and whose simplified (p. 1) and typical (fig 22, p. 25) application schematics match what you started to sketch.
We've got a winner!:D Thanks so much, just out of curiosity @tooki how were you able to guess it? I find it so hard to get the right part number from these codes.
Even right now I'm struggling to find the part number for code 'AGCG' its an SOT 26 package. I know its some kind of voltage regulator or buck converter used to derive the 3.3V power rail. I have searched so much no luck
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On a different note:
I might have figured out why the unit I have is failing to power up. The capacitor at pin 2 (C1) seems to be open. I have removed and checked it, could that capacitor being open have caused the unit not to power up? Now the problem is I don't know which capacitor value to replace it with. The example circuit on the data sheet says 3.3nF - what would happen if I go above it? I recall that the unit takes quite a bit of time to start up from the initial 'all led on'.
Thanks for the help again