USB-C 3A @ 5v? - Page 1
Forum section: electronics / projects

author: hfern
author_rank: Newbie
timestamp: December 28, 2019, 11:33:49 pm
content: Hi there!I am working on a project where I want to fire a mini Push/Pull Solenoid and power it through the a USB-C Breakout board & the official Raspberry Pi Foundation USB-C power supply (which says it will support 3A @ 5V).The problem I am having is that I am only able to draw 0.6A out of it -- and when I do I experience a voltage drop between VBUS and GND from 5.2V down to 4.25V. This is a problem because I want to also power a Raspberry PI Zero W on this same circuit and it requires 5V. The product details on the Adafruit page says I should be able to draw at least 1.5A from the USB-C breakout board and the power supply says it can supply 5V @ 3A.The USB-C breakout board I am using isthis Adafruit one. I have also tried the sparkfun one and I am seeing the same limitation. I have tried both the Raspberry Pi power supply and an Apple USB C supply.Here's my simplified circuit:And here is the voltage drop that occurs when the solenoid is activated with the button:Here is the draw in amps when activated:The voltage drop is not temporary, it lasts as long as I keep the solenoid activated.I suspect this is due to the default USB supplied power of 500mA @ 5V = 2.5W. This is suspiciously close to my measured amps * lowered voltage of 0.63A * 4.248V = 2.68W.Here is a picture of the test setup I am using. I added and LED as a little indicator:Here's what I've already attempted to troubleshoot:- I've verified that there is 5.1k Ohms between CC1/CC2 and GND. The breakout board does this -- I just wanted to verify. TheUSB app note linked by Adafruit on the board pagesays this will give at least 1.5A (Section 3.2, Table 7).- I've measured the voltage between CC1 and CC2 and it's 1.77 volts. The above document indicates (SS 3.6; Table 9) that this means that the power supply is advertising up to 3A, which we expect. So.. why can't I draw that?- I've tried shorting D+/D- as I've read online this can indicate desiring a higher current. It didn't work!Can anyone help me figure out why this thing is not supplying more power? What am I doing wrong?I am hoping one of the folks here is knowledgable enough in USB.

author: pigrew
author_rank: Frequent Contributor
timestamp: December 29, 2019, 01:35:06 am
content: I would first suspect the cable is causing the voltage drop. Normally it is supposed to be a max 0.75V drop when loaded.Can you try a different cable, and perhaps measure the resistance of the Vbus and GND wires?You could also cheat cable resistance a little bit by shorting GND and SHIELD together.USB-PD might be needed in your case, or perhaps a 5A USBC cable (which would have lower resistance)

author: bson
author_rank: Unknown
timestamp: December 29, 2019, 01:36:34 am
content: USB 2 will give you 500mA, USB 3 900mA. Anything else requires negotiation using the CC pins, using USB Power Delivery.(Edit: this is assuming you tried with 22kΩ or 10kΩ pullups on CC1 and CC2. Those aren't in your circuit though.)

author: hfern
author_rank: Newbie
timestamp: December 29, 2019, 06:51:54 am
content: Quote from: pigrew on December 29, 2019, 01:35:06 amThe cable is built into the power supply and the power supply is rated for 3A @ 5V. I've also tried it with an Apple USB-C charger and the Apple cable and I've seen that thing send a lot of power to a macbook.Quote from: bson on December 29, 2019, 01:36:34 amIt was my understanding that the 22k and 10k pullups would be on the source (the power supply) -- I am looking atthis chart (page 5 / table 2). So since my device is consuming power I would be the sink. So Table 3 there indicates my side of the USB C connector should have 5.1k pulldowns -- and indeed the USB breakout board does!Table 4 seems to indicate that I can get 1.5 or 3 amps without engaging full USB PD. It has 1.5 and 3amp under the mode of operation "USB Type-C current at 1.5/3A" which is distinct from another value of "USB PD."Thank you guys so much for helping me out with this!I am new to USB so please correct me if I am missing something!