Is the BB Black really intended to be powered by the USB?

I was wondering if anyone else has noticed strange power-related issues when powering via the USB port?

I was attempting to play around with the PWM pins and so I wanted to make sure that I was getting the proper power from the board before I hooked it up to some LEDs. I used my multimeter to try and read the voltage levels from the P9 pins. I found two things that bothered me.

  1. The SYS_5V pin was only reading around 4.5V

  2. As I checked these pins, the board would randomly just lose power :-/. It happened from both a powered hub and from a USB port directly attached to the PC.

According to the SRM, powering the board from the USB should be fine for most tasks. For now I’m running the board from a 5V/2A supply and it seems to be running fine, but the PMIC gets hot. Too hot to touch and it keeps the entire board warm. The spec sheet says the chip can handle 105 C, so maybe this is normal, but I’m still wondering if there’s something flaky with my board.

Yes it is intended to be powered from the USB. However, you are the supplier of the USB. If your USB can’t supply 5V, well, I guess that will definitely be an issue.

If the PMIC is getting that hot, well, sounds like during your probing process you may have shorted something out. It should not get too hot to touch. If we assume that the 5V form your PC is enough, and when the board is plugged in it drops to 4.5V, then there is some sort of damage that has been done to your board. Not flaky, just busted. As you say you checked the pins and the board would randomly lose power, that is generally not good. Sounds like some sort of shorting is taking place.

I would check the current flow from the 5VDC supply and see what it is taking. Reply back and I will tell you if the reading is out of whack.


Unfortunately, I don’t have the tools available to measure current :(. I’ll ask around to see if I can find a buddy with a way to measure current. (Or maybe there’s enough junk in my drawer to make one with an Arduino).

As for the PMIC getting hot, that is with it sitting idle but I am using the ethernet port. When it was connected using USB, I wasn’t using the ethernet, just probing the pins. I checked from two different USB ports, one was a powered hub from my monitor, and the other was directly off my linux server. I would be really surprised if it’s not up to par, but if I can measure the current, that should confirm what’s going on.

~ Jason

Most likely you have damaged the board. I would ask for a temperature but I doubt you have a measuring device. On all these parts if you hold your finger on it for a long period of time the skin will heat up and it will start to feel hot. If you put your finger on it for 2 seconds and it feels hit then it is. Is the processor hotter than the PMIC?


Ouch, I feel like I’m being scolded.

I’ve ordered a decent multimeter so I’ll be able to take some accurate current readings in a day or two. As for temperature I have a infrared thermometer that I can use, obviously not that exact, but it can usually get in the ball park. I’ve booted the board and it’s running off of the supply. Nothing else is hooked into the board.

after 5 minutes: PMIC ~ 125F, ARMv8 ~ 105F
after 10 minutes: PMIC ~ 125F, ARMv8 ~ 110F

Plugged ethernet in, SSH’d in, and ran top, CPU is around 98~ idle

after 15 minutes: PMIC ~ 135F, ARMv8 ~ 115F
after 20 minutes: PMIC ~ 140F, ARMv8 ~ 125F

If I broke the board, I would love to know where I went wrong. I’m more than willing to fess up when I’ve made a mistake. I’m not an EE but I’m not new to electronics and I generally try to be very careful when working with boards and ICs. No, I don’t wear an anti-static wrist strap at all times, but I also don’t just go shortly pins to see what would happen.

I ma not trying to scold. I just need information to try an prevent what I am gong to say in the next sentence. So, I suggest you request an RMA so we can look at it at the factory to determine what has happened to the board.