On Wed, Mar 2, 2016 at 12:15 PM, Jakub Kákona kaklik@mlab.cz wrote:
Hello,
I take look on the bq24193's datasheet and I think it is almost perfect IC for intended application.
good to hear. there are some variants btw - bq24192, 24191, 24196 - it would be good if you could double-check which one is best. the USB-OTG functionality @ 3A is *critical* because EOMA68's 5V power rail is *REVERSIBLE*. basically you can either *PROVIDE* 5V power or the CPU cards can be *PROVIDED WITH* power.
so i am using the USB-OTG rail of the bq2419x series to provide up to 15W of power to the *entire* laptop.
STC3115 seems to by quite cheap but not the best solution.
We currently have quite outdated, but still better battery gas gauging design based on BQ34Z100.
if you've got something better, _great_.
Documentation is here http://www.mlab.cz/Modules/PowerSupply/LION1CELL01A/DOC/LION1CELL01A.pdf
looks great. it's almost the right size as well.
I think the main work should be the redesign of our LION1CELL01A module with bq24193 charger integrated in it. We should do it in KiCAD probably in form of new MLAB module (for testing). The exact PCB for Libre laptop should be derived from it then.
.... it's almost perfect as-is. if you can keep the bits which should not go into the laptop on a snap-off area along the bottom of the PCB then it's pretty much done already.
Is current blocks/circuit schematic of Libre laptop somewhere?
honestly... you're the first person ever to ask. i'll generate some schematic PDFs and point you at them shortly. i will also document the pinouts of the various connectors, as that will be part of the specification for the Power PCB.
I do not understand how the higher voltages (+5V) or +12 (for LCD) are efficiently generated from battery?
the LCD is only 4 watts (despite being 15.6in), backlight is around 3W, and when run at only 30hz the LCD uses under 1W. a single simple step-up converter to around 17-20v @ 150mA constant current is therefore perfectly ok, from a 5V supply.
this is *not* a monstrous "let's burn the user's eyes out with a 20W backlight and dazzle them with 5W worth of 3480x2000 pixels @120fps needing 5GHZ worth of bandwidth".
so i've used a Silergy SY7201 (or equivalent), it's a SOT23-6, it's got a power dissipation rating of 0.4W - it does the job.
+5V comes from the USB-OTG function of the bq24193. that can provide up to 3A, which is perfect, and is exactly what's needed. so there is no need for a 5V regulator.
the "normal" power output is battery-level (4.2v) and does *not* need to be stepped up. it goes straight (solely and exclusively) to PCB2 - the "Embedded Controller" board. this is actually a 3.3v part, so there is a 3.3v regulator.
basically the EC board - which manages power, keyboard, touchscreen, and provides RTC functionality etc - is the *only* thing which needs continuous power, so that's run off of the bq24193's "main output".
the EC board is where the I2C interface goes [NOT to the EOMA68 CPU Card!]. so it is the EC's job to perform "on / off" function. the *EC* controls the CPU Card's power state. the *EC* tells the bq24193 to switch the USB-OTG power to 5V @ 3A. the *EC* listens to the battery status (from the bq34z100).
basically, this is *not* a "standard laptop", it's an "embedded" design. so there is no 5V rail, and there is no 12V rail: embedded power ICs for single-cell applications can therefore be considered.
Has this design higher efficiency than two balanced cells connected in series?
given that the maximum power required is only 15W, which is within the budget of the bq2419x series, i am more concerned about simplicity of design (and completing this product) than i am about running efficiency. a 2-cell design is far more complex to design - apart from anything, 2 cells would need to be sourced of exactly the right size, and it took me months to find even the current battery.
later however, once this first laptop is out the door, i will begin a 2nd design which will need something like a 30 to 35 watt budget (more USB ports, built-in SSD, etc.) and at that point a 2-cell or 3-cell design is going to be needed. however, the implications for that design decision are MASSIVE. the casework - which has already taken well over a year to complete - would need a total overhaul.
l.