Uwe Klein wiederling at googlemail.com
Wed Aug 20 11:05:41 CEST 2008

On 8/20/08, Andy Green <andy at openmoko.com> wrote:
>  Hash: SHA1
>  Somebody in the thread at some point said:
>  | On 8/19/08, Joerg Reisenweber <joerg at openmoko.org> wrote:
>  |
>  |> This power removal is done by U1705, and it should relyably cut power
>  when we
>  |>  disable IO_3V3 what is quite normal for shutoff.
>  |>  No special kernel action required.
>  |
>  | This is in a lot of cases a faulty assumtion.
>  When IO_3V3 goes down it goes down... the pcf50633 has special
>  arrangement to bring down "off" regulators to 0V.
( Hmm, pull down seems to be only on the LDO regulators 4,5 : 0.8R
all others : 2k
GSM sits on one of the switchers? )

That does not make that much of a difference.

The chip is (partly) supplied via the IO pins when they are at H level.
You have to accertain that no protective diodes internally go from the
relevant IO pins to VCC ( VDD, whichever.).
I have seen a couple of hundred mVs beiing  sufficient to
keep (broken) state.

Another solution is to take town to logic Low the lines to that chip
before powering off.
In most cases using the dedicated Power Down pin is the better
solution.  Its function is "designed in".


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