[TriEmbed] TriEmbed Digest, Vol 44, Issue 27

[Brian]

I'd be interested in seeing a high-resolution (>= 1Msps) look at the 
power rails over the course of a few seconds.  It's the fast transients 
that can really wreak havoc.

What's the ripple on your buck/boost output?  Set your scope somewhere 
around the switching frequency (e.g. for a 400 kHz switcher, use around 
2 uS/div) and have a look on both sides of the LDO feeding the ATmega. 
What's the LDO's dropout voltage?  With a Vin of 4.0V and a Vout of 
3.3V, that's not giving the LDO much headroom.  Definitely measure under 
all modes of operation, as well as during the crossovers between 
supplies (solar->battery, etc).

HTH,
-B

PS: You shouldn't need to change your reflow profile appreciably after 
removing thermals; the whole idea is that everything is coming up to the 
same temperature more-or-less together since heat is being applied from 
all directions.



On 01/24/2017 09:10 AM, Chip McClelland via TriEmbed wrote:
> All,
>
> Thank you for the great suggestions.  Based on your responses, here is
> what I am thinking:
>
> - Given the number of “events” and days over which the counter runs, the
> issue is likely hardware not software
> - I checked the fuses on my Arduino and I do have brownout protection
> turned on.  I am running at 8MHz, 3.3V and brownout is set to 2.7V
> - The ATMEGA 328p can run up to 10Mhz at 2.7V so should be good there
> - I took two hours of measurements at 1/2 second intervals while the
> device was under test out of the 14400 test points - average 3.282V and
> lowest was 3.279
> - I have taken a screen shot of the test here
> <https://dl.dropboxusercontent.com/u/21074878/Vcc%20Log%20over%20two%20hours.png> I
> think that this looks fairly clean but please let me know if you see
> anything that needs more exploration here.
>
> I did find more noise and voltage sag under load in my Solar power
> converter than I expected.  I contacted TI support and they suggested I
> change my layout.  You can see the exchange and how I have improved the
> layout here
> <https://e2e.ti.com/support/power_management/non-isolated_dcdc/f/196/t/569106>.
>
> I am now wondering if there is some dynamic between the Solar Panel
> board and the LDO converter on my trail counter.  I plan to start
> testing this once I figure out how to do so.  It may be there are some
> transients when the Solar Board changes to Solar charging, LiPo battery
> or Solar batter charged.
>
> Again, thank you all for your suggestions, I will let you know what I
> figure out.  I am also going to respin the boards to improve the power
> supply layouts.
>
> Chip
>
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