Author Topic: USB-C 3A @ 5v?  (Read 1998 times)

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Offline hfernTopic starter

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USB-C 3A @ 5v?
« on: December 28, 2019, 11:33:49 pm »
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 is this 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. The USB app note linked by Adafruit on the board page says 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.
« Last Edit: December 28, 2019, 11:37:22 pm by hfern »
 

Offline pigrew

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Re: USB-C 3A @ 5v?
« Reply #1 on: December 29, 2019, 01:35:06 am »
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)
 

Offline bson

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Re: USB-C 3A @ 5v?
« Reply #2 on: December 29, 2019, 01:36:34 am »
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.)
« Last Edit: December 29, 2019, 01:44:32 am by bson »
 

Offline hfernTopic starter

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Re: USB-C 3A @ 5v?
« Reply #3 on: December 29, 2019, 06:51:54 am »
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)

The 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.

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.)

It was my understanding that the 22k and 10k pullups would be on the source (the power supply) -- I am looking at this 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!
« Last Edit: December 29, 2019, 07:38:41 am by hfern »
 


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