Pay no attention to William. You comments are welcome and Gerald has accepted your comments as valuable input by thanking your for your feedback. Now, let me address your concerns:
vary):
1) The power supply used to power the BBB should be selected so that it does not damage the BBB, so a 2A power supply was specified. If you wish to change that specification, then the onus is on you to verify that a 4A power supply will not damage the BBB. Your conclusion that is may damage the BBB means that you should not use a 4A power supply. In addition, a power supply that is specd at 4A should not shutdown when it sees a 4A load, but rather, it should current limit at 4A. If the power supply is specd at 4A, then 4A should not be treated as a short circuit.
I would have designed the power supply circuitry so that with a power
supply of appropriate minimum rating, the maximum rating would not
have mattered. Using a power supply with a maximum current rating to
avoid damaging circuitry is not (again, IMHO) the best solution. If,
because of economic considerations, that decision is made, then it is
imperative of the designer to put this information specifically in the
power supply recommendations. Not doing this leads to damage, doing
this puts the responsibility on the user. Is this a "before the
design/after the design"? I don't know, and I don't remember (either
way) if this warning was ever in the power supply requirements.
Hindsight is 20/20, of course. If it's that important, then perhaps
the documentation needs to be changed. Decision not up to me.
2) The TI spec for the TPS65217C is a general recommendation as they are unaware of how you are going to use the part. The BBB SYS_5V powers several subsystems, including HDMI, I/O (VDD_3V3B) and USB. Clearly you could move the 100uF to the other side of the TPS2051, but then you need an additional capacitor on the SYS_5V which increases the cost and doesnt provide any clear benefit, if you choose the correct power supply.
"correct power supply" bothers me. I'm familiar with minimum current
capacity, voltage limits, short circuit current limits (infrequently
applied). Again, "a 4 amp power supply will allow the board to damage
itself, so we depend on a 2 amp maximum supply to avoid damage." This
could be discussed a bit....
3) As Gerald has pointed out, the BBB is just a reference design. It was designed as a low cost solution which meant that tradeoffs were required to keep the price low. Clearly things could have been done differently, but then the BBB price would have been much higher and the board larger. Given that most users would probably not need these extra features, they were not incorporated into the current design. There are several spinoffs of the BBB, some with wifi, some with more RAM, etc, but none have been as successful as the BBB.
Hmmm, well, perhaps (although not required) it might be nice to know
what the engineering limitations are of the design.
I've seen 1) the ones I know about, and 2) the ones I haven't found
out yet... and 3) the ones people are going to have to tell me
about...
and I do like paranoid designs.....
Harvey