Am Mo 30. Juni 2008 schrieb Andy Green: > Somebody in the thread at some point said: > | Andy Green wrote: > |> Anyway the main battery + pin shows no signs of any dents or load and > |> sits there at about 0.4V itself before during and after the fun on Vsys. > |> ~ I don't think this can be it. > | > | I added an 100uF bypass to VB_SYS and a 470uF capacitor where the > | battery ought to be. That monster didn't impress the system at all, > | and it happily continued to run. > > Now my backup battery has charged up (to ~1.3V), the behaviour changed, > I couldn't hear the ticking sound from the mic any more but it is still > spinning with Vsys trouble. However the Vsys broken part is much more > variable and can oscillate -- the attached pic shows a 250us outage > happening at low probability. > > | I then just shorted the battery. That got me some "motorboat" > | effect. So the battery isn't completely ignored. > > I also tried to hook VBUS (USB +ve after the host switch) to the Main > battery +, it starts beautifully. But a LOT of current is pulled that > way, hooking it to the battery + via 5R did not help the symptom, a > chunk of wire did. So the system tries to pull >2A I would guess from > Vsys starting the whole disaster. Where is all that current going! > > It's a strong indication USB power is disconnected from Vsys by the PCF > due to USB overcurrent as suspected, we fill in the hole from the > "battery" and we go on. > > | I'm confused :-( > > It all comes down to where is all the current going at startup. We'll > get unconfused real quick when we work that out. The regulators are > current limited during this phase and shouldn't be able to add up to > ~10W that is suspected. It seems the culprit is via Vsys path not via > battery directly.
The auto_converter powering IO_3V3 is designed to deliver high current, and in step-down mode probably even might draw way more than 2A, to charge C1707 (47u) and dunno what else. I wouldn't rely on current-limiter of this regulator on startup. To test it might be a simple setup to feed some 3V to IO_3V3 from external powersupply, thus precharging all these Cs - dunno if this would terribly spoil anything on startup. However the test is so simple it might be worth it. /jOERG
signature.asc
Description: This is a digitally signed message part.
