Re: [Gumstix-users] Rechargeable batteries for night-long operation - also LOW_POWER mode?

[Dave H. <dhy...@gm...>]

Hi Doug,

On 12/16/05, Doug Sutherland <do...@pr...> wrote:
> Dave Hylands wrote:
>  > At work we have an external power management chip that allows us to
>  > turn on and off a whole variety of voltages for various subsystems.
>  > This allows you to save more power than the idle mode, but not as much
>  > as sleep mode.
>
> Is this in off the shelf superivor IC or something you designed for
> your own needs? Any recommendations?

It's a PMU chip. Something like this:
http://www.semiconductors.philips.com/pip/PCF50604HN_03_2C.html
(We're using a slightly different model number, but the basic
functionality is the same)

Power consumption is proportional to frequency times voltage squared.
Frequency scaling in and of itself generally doesn't buy you much
because it now takes longer to do everything. There is a bit of
savings as you lower the frequency down to your memory bus speed
because you're now spending less time waiting for memory, but this
depends on your cache hit/miss ratio. The real power savings come when
you can lower the voltage, which typically requires lowering the
frequency.

--
Dave Hylands
Vancouver, BC, Canada
http://www.DaveHylands.com/