[Arm-netbook] EOMA68 laptop battery management.

[Luke Kenneth Casson Leighton]

On Wed, Mar 2, 2016 at 4:25 PM, Jakub Kákona <kaklik at mlab.cz> wrote:
> Hi,
> It looks like power schema I expect that is already been done.

 it hasn't.  you're missing some history (dating back several months).
the LTC4155 was chosen because the datasheet *CLAIMED* that it was
compliant with USB-OTG power provision.  however, what they neglected
to state was that USB-OTG power is *DISABLED* when a 5V DC input is
plugged in.

 basically, replace LTC4155 with bq24193, and STC3115 with BQ34Z100.

 the only complication is that there will need to be a bi-directional
Open Drain level shifter to convert the GPIOs for the bq24193.  e.g. a
TXS0104E.

 why is a level shifter needed?  because the bq24193 operates its GPIO
at 1.8V, and the STM32F072 operates its GPIO at 3.3v.  so the I2C and
GPIO signals from the bq24193 need to go through a level-shifter.  it
needs to be bi-directional because SDA (I2C data) is bi-directional.

for the BQ34Z100, apparently it can take REGIN as a reference voltage.
so, for this, the Reference Voltage from the EC board (VREF_3V3)
should be hooked directly to this pin.  that takes care of the GPIO
voltage levels for the BQ34Z100.


>  But a
> current design is still not fully clear to me.

 as this is a complex inter-dependent 4-PCB design with 18 months of
design work in 3 of the PCBs and 4 years design work in the EOMA68
standard, that is not surprising.

 however, fortunately, the only part that you need to be absolutely
clear on is the Power PCB.

 if you'd like me to fully explain the full design i'm happy to do
so.... just bear in mind that it may take some time.


> I will probably print the schematics PDFs on large A3 sheets tomorrow and
> try to find out how the Libre internals are interconnected currently..

 by then phil should have had a chance to update the wiki and bring it
out of broken-ness.  in the meantime i'm attaching the pcbs.mdwn page
which contains the specifications of the connectors.  you only need to
be concerned about PCB2-to-PCB3 and PCB1-to-PCB3.  PCB1-to-PCB2 is for
how the EOMA68 CPU Card and the Embedded Controller talk to each
other.

l.
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