Tony Duell wrote:
As a bare
minimum, if I made a kit, I'd want to supply it with the power=20
controller chip soldered down (the aforementioned QFN chip -- TI=20
TPS75003). That's simply because the leads don't extend up the side of=20
Is thatere any particular reason that you're using this chip? I haven't
got the data sheet, but what does it do that can't be done with
easier-to-solder components?
The FPGA needs the power to be sequenced in the order:
VCORE up
short delay
VIO up
another short delay
release RESET and load microcode
Additionally, there is a minimum and maximum ramp rates for VCORE and
VIO; go too slowly and the POR doesn't work properly, go too fast and
the FPGA can "potentially enter a latch-up situation" according to the
datasheet.
It's far easier to just use a solution that Altera have given the
rubber-stamped seal of approval to. In this case, it also costs less
than half of what a similar design using standard SMPSU controller chips
(e.g. something from the NatSemi Simple Switcher series) would cost.
So effectively I'm getting to tick three boxes:
1) It's less likely to Blow Stuff Up
2) Altera say it'll work with the FPGA chip, thus I get to yell at
them if it doesn't. Also TI are saying it'll work, and they provide a
reference design for the chip I'm using, which is another bonus.
3) It's Cheap. Cheaper, in fact, than the 5V pre-regulator (the NSC
Simple Switcher part).
But in exchange I can't tick this box:
4) It's easy to solder the chip down to the PCB
So it's a trade-off. Alternatively I can get a chip that meets criteria
(4), but not (1), (2) and (3). Also, FPGAs are expensive -- you
generally don't want Bad Things to happen to them!
The hard (or at least expensive) part is going to be dealing with the
EMC regs... On the plus side, the 12V input means it's exempt from LVD
regs ("that would be the power supply manufacturer's problem, not mine")
Firmware source listing?
On the website and a CD-R that I plan to include in the box :)
FPGA souce? PAL/CPLD equations?
No PALs or CPLDs, but the FPGA source is included with the MCU source.
I can assure you that if parts being NLA stopped me
from repairing
something then many of my classic computers wouldn't be operational.
8^)
--
Phil.
classiccmp at philpem.me.uk
http://www.philpem.me.uk/