Am Di 1. Juli 2008 schrieb Andy Green: > Somebody in the thread at some point said: > > |> | To test it might be a simple setup to feed some 3V to IO_3V3 from > |> external > > |> Gah I read this as I just finished doing that test on STBY_1V2, 1V8 and > |> IO_3V3 rails from a second A5 that was powered first -- the first two > |> make no difference, but we get a good start on the unit under test if I > |> gave it "3V3 transfusion" from the other A5. So good idea! > |> > |> This is clearly a big clue, but our PMU variant says that it current > |> limits the Auto regulator to 400mA during its startup. > | > | had no look at the particular power-up sequence. So just an idea: > precharge > | via a diode from some low-power lower-voltage more-early-in-sequence > | regulator? > > There is no sequence on our PMU variant, it all comes up on "activation > phase 3" in a big lump, which doesn't help anything. Except STBY_1V2 > which is on an LDO off 1V8 and doesn't come up until 1V8 is 1V6 and > more. But the transfusion test on that seems to show it isn't relevant. > > I didn't understand why we appear to have large alleged-inrush current > at startup particularly on 3V3 rail. I tried to remove the 47u last > night to see about the cap charging idea and managed to trash some > components around it :-( so I can't test this idea that the inrush is > coming from ~60u or whatever on 3.3V. But at the time of the problem > the voltages are ramping slowly and do look constant-current (the ramp > into C is linear). The voltages are at around 1V but we pull estimated > ~10W on the regulator input side, it suggests instantaneous inrush > current up at ~10A since we are only at 1V :-/ But the current limit on > the 3.3V rail set at 400mA means we should only suck down 400mW there. > > -Andy >
Test on R1721 (0R). maybe make this 1R / 10R for test purposes If we see current spike on this PMU-power-out, the current-limiter is crap, and we (almost) know where the root cause(TM) comes from. ;-) /jOERG
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