>From the Tuesday design review I still have the following redlines to work on:
Ensure all devices follow the Rocket Names naming guidelines.
Ensure that all lines in the schematic have properly descriptive names.
Run BOM and prepare a parts list (ensure all parts carried over from prior
design are still available).
The current schematic is in git, under the "lv2-node5" directory as
"node5-frontend-rev_2.sch"
There are also the following 7 items that I would be happy to have feedback on:
1) U281 Binary ripple counter used to divide the 12MHz clock down to 1.5MHz for
sync of the SPS and HAP switching regulators.
Issue: At 5V for VDD the part can only handle a max input frequency of
3.5MHz. The specified part can handle up to 12MHz, but only with Vdd=15V.
Solution: Replace with a 3.3V, 12MHz (or higher) divider circuit. Perhaps
similar to the SN54LV163A (binary counter, fmax=50MHz @VDD=3.3V, use Qb and
clock) from TI.
2) CAN transceiver: MCP251x
Issue: Not a 3.3V part.
Solution: Replace with 3.3V CAN transceiver. These are hard to find, but
it looks like TI makes a few, though none in a package smaller than 8pin SOIC.
A good choice appears to be the SN65HVD234 from TI
3) U283 Reset controller, used to hold the reset signal until the SPS or HAP
has reached stable output
Issue: Is this part and its associated circuitry needed?
Solution: Just like the LPC1248, the LPC2368 has brownout circuitry built
into the IC. That said the justification given by the 2006 Capstone team still
appears to be valid.
4) U282 USB transient noise suppressor
Issue: The part is an SOT23 package, not DFN. That said the SOT-6 is still
a pretty small part, just not leadless.
Solution: Possible to look up a new part available in a DFN package. The
existing part is available in SOT23, BGA, SSOP, and PDIP.
5) Small "cut-able" jumpers
Issue: in several places, there are small cut-able jumpers in the
schematic, is there a standard symbol for this? Is it a good idea to cut traces
on the board in the first place?
Solution: Use two zero ohm resistors, mark one as a do not place. If
desired, resistor can be removed and soldered on in the alternate position,
resulting in lower possibility of board damage and higher reliability during
use.
6) USB High Speed Select
Issue: Can the LPC2368 drive the voltage and current needed to get the bus
to act in High Speed Mode?
Solution: Probably, Need to look up the USB2.0 spec to be sure. The LPC2368
can output +2.9V (VDD-0.4V) at -4mA on its GPIO pins.
7) Everything Else
Issue: Time consuming
Solution: Time machine, I checked, TI still doesn't make one, neither do
Micrel, Linear, On-semi, IBM, or Intel.
Thanks,
Ken Z (capstone2009)
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