[onerng talk] Normal Board Temperature?

[Paul Campbell]

On Mon, 15 Jun 2015 13:57:16 brouhaha wrote:
> Another friend with more switching regulator experience looked at the board
> and suggested that the inductor may be physically too small. If the
> inductor saturates, that makes the regulator hideously inefficient.

I think it's more that the inductor is too small (in inductance rather than 
size) for the regulator and the regulator is not cutting off before it 
saturates - it's wasting current thru its internal power fet

> I also suspect that the lack of a bulk capacitor on the input to the boost
> regulator is likely to make the 3.3V supply noisy. Ideally there should be
> at least a 4.7 uF capacitor. Is there any particular reason why no bulk
> capacitor was designed in, and why the input to the boost regulator input
> is from the 3.3V rail rather than Vbus?

We actually tossed a couple of parts we were offered because they trashed the 
3.3v rail, this was definitely the cleanest, the bit of noise that's there on 
the digital supply isn't an issue, the analog portion has an LC filter and is 
quite clean.

The basic circuit doesn't really need a bulk cap because it's fed directly 
from the regulator -  we're pulling less than 1mA from the boosted voltage, on 
the AP3015 circuit this means that the boost reg needs little in  the way of 
input caps (except during startup when we're not looking at the output)

> My unit works fine, so none of this should be construed as a complaint, but
> I think if a few changes were made in a future production run, it would
> result in improved long-term reliability.

I think when we build more we wont buy these parts in China :-) buying there 
is difficult, I have a local purchase agent, she did a great job with the CPUs 
getting a great price, the same with all the other parts she bought except for 
this one. The original hand built parts used the AP3015 which runs cool and 
happy.

> My unit works fine, so none of this should be construed as a complaint, but 
I think if a few changes were made in a future production run, it would result 
in improved long-term reliability.

I agree - we've had no reports of actual failures - but we wont use this part 
again, I'll eat the cost and buy a better defined part we trust

	Paul