next-generation PMU discussion
werner at openmoko.org
Sun Apr 20 17:37:04 CEST 2008
joerg at openmoko.org wrote:
> with standard battery we get a standby of 1200 / 0.6 = 2000h max. Sounds quite
> neglectable, but like Andy said, every bit of current counts. It's all
> summing up.
Whoa, that's the MPU going full blast all the time. SETI at MPU, here
we come ;-)
If the MPU can sleep every once in a while, we get a low-power mode
that's about three orders of magnitude more battery-friendly.
> We can handle this. Have the MPU at some booster that's to be leveled down
> from e.g. 3.0V default to sth like 1.8V, what is task of the MPU to set up
Yeah, with an LDO, we'd just burn the power elsewhere, so it should
be a switching supply if we really care about power consumption there.
Not sure if there's anything really nice and small out there, though.
Maxim have a bunch of boost converters that don't look too bad, e.g.,
the MAX867EUA+T  (3.3V, 3x5mm footprint). Needs external caps,
inductor, and diode.
The tiniest I could find is the TI TPS62700YZFR  (3.09V or
adjustable 1.6x1.5mm), which doesn't even need an external diode. But
it's not cheap, and it burns 300uA on its own, basically negating any
gains we could get.
> All the other chips will have additional FET-low-R switches (one for
> each powerline that need it) to protect them from OV
I don't think the PCF50633 ever pulls strongly to GND. It normally
uses a weak pull down if the regulator is off, though.
> Some VoltageDetection for PowerGood if we can spend.
So far, we got away with what's inside the PMU :-)
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