Not seeing power over USB - Page 1
Forum section: electronics / projects

author: Jonathon_Doran
author_rank: Regular Contributor
timestamp: August 16, 2024, 06:24:38 pm
content: I just got my boards in from JLCPCB, and they look fine. I rang them out with a multimeter and didn't see any problems.But applying power over USB and I did not see anything on the testpoints.I verified a connection between the USB connector VBUS pins (both of them) and my VBUS test point. I took a USB cable and chopped off the head so that I could break out the lines. I verified that ground and VCC go to the appropriate test points. I plugged my cable head into a USB power hub and verified +5V on the appropriate wire.So why would I not see power on my board?The schematic (which I posted earlier for review) has both CC lines pulled down through 5K1 resistors. That shouldn't matter on a power only cable (I would expect it to supply power at all times). D+ is pulled up to 3.3V (hmm that might be a problem), but again that shouldn't matter on a power only cable.Any suggestions on how to troubleshoot this?

author: Nominal Animal
author_rank: Super Contributor
timestamp: August 16, 2024, 07:18:33 pm
content: Quote from: Jonathon_Doran on August 16, 2024, 06:24:38 pmWhat's the resistance between VBUS and GND on your board? Maybe there is a short on your board.

author: Jonathon_Doran
author_rank: Regular Contributor
timestamp: August 16, 2024, 07:27:53 pm
content: No connection.I rang out these values before applying power.But I assure you I checked it again with a multimeter now. Edit: OVF (My earlier "nothing" could be misinterpreted as 0-ohm).Thanks for the suggestion.

author: Benta
author_rank: Super Contributor
timestamp: August 16, 2024, 07:56:15 pm
content: How much current is your board supposed to pull?The hub won't supply more than 100/150/250 mA without negotiation.

author: Jonathon_Doran
author_rank: Regular Contributor
timestamp: August 16, 2024, 08:37:45 pm
content: A lot of crazy stuff is going on now. I appreciate all suggestions as it is causing me to check things.The MCU tops out at 150mA. There is a power LED on the board with a 1K5 resistor, so the LED probably pulls a couple of mA.This is consistent with my being able to power the board off of a power strip with USB ports, as well as a USB-A port in the back of a computer. A USB-C port on the computer does not power the board up. Nor will the USB-C port on the power strip.I do not attempt any negotiation. Both CC lines on the USB connector are pulled down through 5K1, and the D+ line on the connector is pulled up to 3V3.One really good thing was that when I powered up the board from the USB-A port on the computer, I got an unknown USB device message and saw the board in device manager. I just got these boards, so I have not soldered switches in yet. The bootloader switch is pulled up (this is an STM32F series MCU), so I believe that puts it in program mode.I thought I tested the USB-A side before, but I honestly do not know what type of cables these are. I hate that I cannot tell by looking at them. These may be power only, or data cables.

author: artag
author_rank: Super Contributor
timestamp: August 16, 2024, 09:56:40 pm
content: Quote from: Jonathon_Doran on August 16, 2024, 06:24:38 pmA PD-capable USB-C power source will not provide power unless the CC lines are configured as you have stated. So yes, it should work but IS required. However, I don't know what the D+ does for power. Is that from an earlier standard ?A quick way to check if it's negotiating wrongly (I'm including passive pulldowns as negotiation) is to get a cable that has USB-A at one end and USB-C at the other. These are intended to slowly charge USB-C phones from a USB 1.1 or USB 2 charger. They have few benefits but one is that they don't do any negotiation, they just dumbly provide power. Sometimes they have data and sometimes they don't. If it works with that instead of a proper USB C PD charger, it's likely something with your negotiation that's at fault.For what it's worth, I use two 5k1 resistors as you describe and nothing on D+ and it works for me on all the chargers I've tried. If done without the resistors (or with just one as a common ebay USB C breakout board provides) it will work with a dumb charger and not with a smart one.

author: Jonathon_Doran
author_rank: Regular Contributor
timestamp: August 16, 2024, 10:40:28 pm
content: A USB-A to USB-C cable does work with my board if the USB-A side is plugged into a computer or a power source with sufficient capacity. My board uses a USB-C connector, but only the USB 2.0 signals.I accept that I was likely pulling too much current for the small hub that I tried earlier. A USB-C to USB-C connection does not work for me.Regarding the D+ pullup:Here is a quote from one arbitrary sitehttps://www.beyondlogic.org/usbnutshell/usb2.shtmlA USB device must indicate its speed by pulling either the D+ or D- line high to 3.3 volts. A full speed device, pictured below will use a pull up resistor attached to D+ to specify itself as a full speed device. These pull up resistors at the device end will also be used by the host or hub to detect the presence of a device connected to its port. Without a pull up resistor, USB assumes there is nothing connected to the bus.I see the reference that I used for my board: AN4879 from ST, section 3.1 has the 1K5 pullup.Do you use DFU, or send data across USB? I need to do both.

author: radiolistener
author_rank: Super Contributor
timestamp: August 16, 2024, 11:15:09 pm
content: USBA to USBC cables usually have some IC inside USBC connector. It prevent feeding power from USBC to USBA. It works at single direction only: USBA to USBC.So, if you connected USBC to power supply and want to get voltage from USBA, you can't. It can show some voltage with no load, but once you connect even a small load the voltage drops down to zero.You can detect such cable by measure resistance between cable VCC and GND, for calbe with IC it will be about 61 kΩ.

author: Jonathon_Doran
author_rank: Regular Contributor
timestamp: August 16, 2024, 11:35:35 pm
content: I'm trying to go the other way around. Power delivery to the USB-C connector. From either USB-A (via a USB-A to USB-C cable) or direct from USB-C.I would like to get the USB-C to USB-C working. I could add in a USBC power delivery chip, and that should take care of the complex case. But would that then keep me from using a USB-A adapter cable to move power and data that way? I don't need either the power nor the fast data of USB-C, I was just trying to future proof things a bit.