Have you checked the System Reference Manual for information on the battery?
It uses the TPS65217C. Generally speaking you can use it to run from and charge a battery. No the USB host will not work because it has no 5V supply, only the voltage supplied by the battery.
Yes I’ve just walked through the BOM and found the power management unit (PMU). I thought the PMU was able to ramp up the voltage with it’s DC to DC converters. But what you are saying is, that everything should actually work, except that I can’t expect to connect an USB device to the host port (as the voltage would be to low).
I’m planning to use a WiFi dongle as well, so this may not be a good idea then, unless the WiFi module runs fine on a lower voltage - maybe worth a try.
Actually I think what he is saying is that you cant use the USB host to charge the LiPo battery because it does not have a 5v supply coming to it. If the USB host is being powered by the battery, the battery would be trying to charge itself. You can use the TPS65217C to charge the battery but you would have to plug in the BBB for the battery to be charged because of the way the PMIC cycles power sources. It detects and uses the most prominent supply first. For instance, if you hook up your BB with the included USB cable, then the PMIC will default to usb power, but if you were to hook up the USB and the 5vDC supply at the same time, the PMIC will default to the ac source until it is removed, and then it will switch to USB power again in the absence of the 5vDC supply. Then if you have a battery, you could unhook the USB and the PMIC will switch to battery power. But you can’t be running off the battery and charging it at the same time, unless you have an external charger, or you could plug in your 5vDC supply and use that to supply the charge for the battery using the TPS65217C’s Li+ charging feature. Or you could probably charge it using the microUSB but it would likely be really slow because you’ll be limited to 500mA.
Are you thinking of connecting your battery thru the TP5-TP8 battery access pads, or through the pins on the headers? I was looking into adding a battery backup via the battery access pads, seems pretty straightforward, but the SRM really thinks you should memorize the entire TPS65217C datasheet before trying it, so maybe it is above my head and i just dont realize it.
Thursday, May 30, 2013 5:15:31 PM UTC-5, Kenneth E. wrote:
I meant DC source not AC…
I don’t expect any of you to memorize anything. Understand one section before attempting to connect a battery? I consider knowing what you are doing before you do it to be a wise position to have. Especially when dealing with batteries!
I absolutely agree. I was just joking about it how insistent it was that i go read the TPS65217C datasheet…it was actually a quick read and quite informative. I was just trying to throw a little humor in there…
I figured as much! I was just concerned that others may read this and think differently!!
Maybe let the TP65217 charge the battery and hook a boost converter from it to have 5VDC back to the BBB through VDD_5V pins.
Yes, that would work. But, at $45 price point, that is hard to add. These devices require inductors and capacitors and are not cheap. I know. I looked.
Agree. I think those applications that really need battery backup can afford the extra cost on its own cape.
In my case battery backup would be nice so I got an boost converter EVM to try and then maybe add it to my design:
That is the way the current battery cape is designed but it does not use the TPS65217C. We did it this way to allow a cape to be made with whatever battery or charger technology was desired and not letting the TPS6217C be a determining factor of that technology. Allowing a battery on the TSP65217C does allow the board to work under battery, just without the USB host support.