next-generation PMU discussion / Memory 1.8V

joerg at joerg at
Mon Apr 21 00:55:03 CEST 2008

Am Mo  21. April 2008 schrieben Sie, Andy Green:
> 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,
> whatever)
> | 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.

Right, if we have to JTAG the MPU to get the board under power, we had to have 
power on some of the boards chips (incl MCU) already. Deadlock ;-P XD 

> 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.

Well we probably don't save much power with sophisticated power design for 
MPU. The idea with a Schottky for feeding the (now) 1.8V to MPU isn't that 
good either. But was only to save another FET. Probably we should hook the 
430 up to Vbat with a lowdrop-linear-regulator. Still wondering about 

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

? more on this later

> 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.

Don't we need the 2.2 for flashing the ROM?


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