[Arm-netbook] A minimal A10 SBC

[Ajith Kumar]

P1

> ---
>
> B1, B2, B3 - call +1.5V "DRAM_VCC" and +0.75V "DRAM-REF", then put 1
> of the capacitors connected directly to the DRAM-REF, and mark it
> "keep as close to DDR3 as possible", to remind yourself.  joe will
> know what value those need to be, but that ref voltage *must* be kept
>

All the decoupling capacitors kept on one sheet for ease of handling, will
note it down in the schematic about the critical positions. Joe is going to
attempt a layout. Could you give some suggestions regarding layers, the
ones to be dedicated for ground etc. My understanding is that there should
be s ground layer next to the DDR3 tracks to get the characteristic
impedance correct and also to give good return path. Something like:
L1 : tracks , L2 : ground, L3 : power, L4 : tracks, L5 : GND, L6 : tracks
Since you already have done it, please make some concrete suggestions on
that.



> A6, A7 - 24mhz XTAL is connected to RTC :)  that'll need to be to N23
> and N22 :)  then, if you are going to have an RTC, you *need* that
> 32mhz crystal - you cannot leave it off.  remember the 10M/1% resistor
> which needs to be put in parallel with the 32mhz XTAL.
>

That was a mistake, intention is to use only the 24MHz oscillator, not the
32k one. Corrected.


> E4, E5 - if the SY8008C is the same as the SY8008B, then you want
> resistors 10x that size, and you want them @ 1%.  so: R10 = 150K/1%,
> R11 = 100K/1%, and R13 = 442K/1% and R16 = 100K/1%.
>

SY8008B or C would do 1A and 1.2A, the resistors calculated as per the data
book. Olinuxino seems to be using 1.1K and 4.99K, I thought it is too much
of current wasted and used higher values. 100k & 1500k will make the
feedback path current 4 micro amps, will it make it more prone to noise.
Should I change it ?


>
> also you're missing the capacitors which *must* be close to the SY8008
> - you want a 10uF on the IN as well as the OUT, but also on the OUT
> you want a 2nd much *smaller* capacitor (joe - 0.1uF?) as this catches
> the high frequencies.  make sure you put these as connected directly
> to the SY8008 because that tells you, when you come to do the layout,
>

The instructions for layout will be marked in the schematic, so that is it
is not overlooked.


to each and every single pin.  my recommendation here: follow the
> example schematic on p5 of the AXP209 datasheet.
>

I did not find an English version, learned somewhat from a lower version
AXP202.


> C7 - what's the 6-pin thing connected to DM0/DP0?  it's not marked.
>

Another mistake, it is only a USB header with two shield pins. Corrected.



>
> other comments:
>
> * no JTAG!  no JTAG+UART equals very very baaad :)
>

Should I add a 20 pin JTAG connector or just bring  TDI0, TDO0, TMS0, TCK0
and RESET to a header. Please suggest.


with regards

Ajith




>
> * joe, what you reckon - a 5V Zener diode on VUSB near the CPU? VUSB's
> range is +4.75 to +5.25.  put a BZT52C5V1S from VUSB to GND?
>
> /peace
>
> l.
>
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-- 
Dr. Ajith Kumar B.P.
Scientist SH
Inter-University Accelerator Centre
Aruna Asaf Ali Marg
New Delhi 110067
www.iuac.res.in
Ph: (off) 91 11 26893955 (Ext.230)
      (res)91 11 26897867
      (mob) 91 9868150852
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