next-generation PMU discussion / Memory 1.8V

Andy Green andy at
Sun Apr 20 20:39:30 CEST 2008

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Somebody in the thread at some point said:
| Am So  20. April 2008 schrieb Werner Almesberger:
|> Andy Green wrote:
|>> I guess if we go this way we have to examine the 50633 defaults closely
|>> to see what the other options are if any.
|> STBYCTL1 and STBYCTL2 don't enable regulators in Standby mode.
|> So we need some other way to get from NoPower into Standby, or
|> give the MPU its own independent regulator.
|> That's why being able to hook it up to battery/USB power would
|> have been nice. But yes, we'd burn a bit of power.
| Hey no problem: we spend a FET (Vbat) and a Schottky diode (Vcore,
| for the MPU itself, so it can switch off it's own Vbat as soon as
there's a
| better supply - like 1.8V from some converter, or maybe the backup bat
| (probably use the one of PCF50633?)
| This way we burn the excessive power only during a few seconds on
MPU-boot /
| PMU setup.

Let's all continue to have a think for a bit.  This is one of those
issues that is mega dangerous and can easily lead to broken prototypes
that don't boot.

We didn't settle on NXP (at least I didn't hear Tony say anything) but I
don't think we can burden the core design with new chips and so on to
solve this.  And I'm not sure about series diodes.

Correct me if I am wrong, but doesn't VSYS see USB power, ie, 5V?  We
can't use that directly if so.

There is a 1.8V in standby because the memory takes it, we can use that.
~ When we need 2.2V not sure what the story should be.

- -Andy
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