[Arm-netbook] A minimal A10 SBC

[luke.leighton]

On Wed, Mar 27, 2013 at 6:12 AM, Ajith Kumar <bpajith at gmail.com> wrote:
> Hello,
>       A rough schematic of an A10 based SBC has been done in Kicad,

great.  right.  let's do a review

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
stable.

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.

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%.

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,
to group those all together.  usually you put manually-drawn copper
joining these together because they need quite thick tracks.

E3 - on the AXP209, you've missed out the capacitors again, which are
shown on all other AXP209 schematics as being very close to the IC and
connected directly on the pins so that you know to put them next to
each line.  for example, you have grouped all the pins connected to
IPSOUT all together, but from that it is *not* possible to tell that
*every* single one of those pins must have a capacitor very very close
to each and every single pin.  my recommendation here: follow the
example schematic on p5 of the AXP209 datasheet.

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

other comments:

* no JTAG!  no JTAG+UART equals very very baaad :)

* 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.