I’m using BBB as a development platform for an AM335x design that will need to run off a 3.3VDC rail, and I have a question about whether that will work with the PMIC. From other discussions, it sounds like the only problem that arises when running the BBB from a lower voltage (battery in most discussions) is that there is no boost to get the 5VDC for the USB host. Is it correct that everything else on the BBB board will run without 5 V power? If so, is there any reason that I could not connect a 3.3 VDC power supply to the BAT inputs of the TPS65217C as suggested in “Case 3” on page 36 of the TPS65217C data sheet?
Any comments are much appreciated.
It will not. Hard to get a 3,.V LDO to work with a 3.3V input. It requires 5V to operate. I could operate down to 3.7V, loosing USB, but that is about it.
No there is no boost in the schematic for 5V,
If you connect 3.3V to the battery pins, it may try to charge your 3.3V supply. You would need to insure that it was turned off in all instances. If you try to fool it to think there is no battery there, it will be tough for the PMIC to switch to it as it has no battery,
As I suspected. That’s what I wanted to know. Thank you very much.
just for the topic. bbb works only with 5v or he has voltage regulator for example 12v - 5v ? I have made a 5v that is actually giving me 5,6v. I am afraid to broke my bbb.
No regulator. See schematic. Raw 5V input. 5.6V is probably OK, but it may be 6V or more if not well regulated and only goes to 5.6V when connected. So check it without a load.
Main issue with 5V is the USB switch on the host port.
Is is 5,6v with or with out load. It those not change. I use 3 voltage regulator l7805 in parallel to see if it works better than one. It works fine with 2 cells. 3 cells get hot. Just one voltage regulator goes to 5,0v. I will just use one l7805 for the usb hub and one for bbb.
I think 7805 needs at least 5.7V. Been a while since I used one.
This is how i use to power bbb:
2 cells = 3,7vx2=7,4v → 7805 - > out 5v - 1a ok
3 cells = 3,7vx3=11,1v → 7805 - > out 5v but it get hot - 1a
2 cells = 3,7vx2=7,4v → 3x 7805 - > out 5,6v - 3a (or may be so) ok
3 cells = 3,7vx3=11,1v ->3x 7805 - > out 5,6v but it get hot - 3a (or may be so)
but all eletronics datasheet said that you should NEVER use parallel voltage regulator.