I am working to create a CAPE for the Beaglebone for use in an
embedded robotic application. The current external power connector
the barrel style, is not very robust in terms of preventing the
power connection from being disconnected (i.e. it is not latched).
The system will be powered by 3S - 5S LiPo battery pack, which
translates into 9V to 22V. I am planning on adding a 5V switcher to
provide power to the CAPE and Beaglebone boards. I am planning on
using the USB hub to connect a Webcam so I will enough power for
some USB usage.
Have you checked on just using a 1S pack and finding an external hub
that's AC wall wart powered and will accept an input that lacks the
power lines (get a cable that just has D+/D- in it)? 1S packs are very
well supported (I run a 1 Ah pack on my bones at times).
Or, find a USB hub IC and put it on your cape, then have a little USB
loop cable up to your cape. Then you can run that hub off 5V from a
boost converter from the 1S pack.
Just throwing ideas out.
So, I was looking at other alternatives. CAPE_5V is the output from
my on board switching regulator. Here are the options:1. Connect the CAPE_5V to VDD_5V => drawback of this idea:if
power is applied through P5 at the same time the battery is applied,
then something is going to get hurt most likely the switch
regulator. I could put in a diode to protect the switcher but then
drops the input voltage to 4.8V - 4.3V.
If your cape is usually right on top of the bone, you could build a
little shield that comes down to block the P5 barrel connector. It
wouldn't work well if the cape isn't right on top, but that's a tradeoff.
Or ship a blank insert for the barrel connector so that people can
install it so they remember not to connect 5V source to the P5.
I think the diode ideas won't work well. Check the undervolt limits on
AC power sources for the TPS65217, I think they're set rather high (ie:
4.3 V or so) and you don't want to be close to that or else you risk
hitting undervolt condition under high current draw transients.
2. Connect the CAPE_5V to BAT on P6 (to simulate a 5V battery) ->
drawback the TPS65217 will try to charge the battery. Again a
diode could protect but at the cost of a voltage drop. It would be
really sweet if the TPS65217 could handle recharging a 3 cell LiPo.
I believe a 1 cell is all the TPS65217 can do.
You can set the TPS65217 to not charge the battery, it's just a
register. It would require a u-boot, uEnv.txt, or kernel board-file
change (just 1 of those would be needed) to support as the default
register setting is to charge the battery. But that shouldn't be that
hard to give instructions on.
Or, you could just not connect the temp sense pin to the TPS65217, or
connect it in such a way that the TPS65217 thinks the pack is over
heated, but I'm not completely sure on the results then. It won't
charge, but I'm not sure (check the data sheet) if it will pull full
current, either.
-Andrew