You are not logged in.

#1 2020-09-16 03:22:09

spaetzle
Member
From: Canada
Registered: 2020-09-16
Posts: 2

USB-C port supplying low amount of power

I've been going nuts with this for a couple weeks now.

I am trying to plug my phone (BlackBerry Key2) into my laptop (TP X1 Carbon 5th Gen). The phone specs say it's compatible with USB Power Delivery 2.0 v1.2 & 9V2A 18W and Quick Charge 3.0.

If I use the original charger or my ThinkPad USB-C 65W charger, the phone charges at >4 volts, >2 amps.

If I plug the phone into the laptop with its original USB-C to USB-A cable, it charges at 4V, 1.2A.

If I plug the phone into the laptop with a USB-C to USB-C cable, the most I get is 4V, 300 mA. That can't be right.

I've tried three different USB-C cables, all (supposedly) supporting USB PD up to at least 60W, one (allegedly) supporting QC 3.0.

Here's the output of lsusb: http://codepad.org/5BrTpXdN
It gives MaxPower as 896 mA, though it's charging at about 1/3 of that.

Meanwhile, when the phone is plugged into the laptop using its original USB-A cable, MaxPower is given as 500 mA, even though the phone is charging at 1.2 A.
Here's the output of lsusb with that cable: http://codepad.org/0jPx8Cxe

AND, if I use that USB-A cable with an adapter to plug it into the USB-C port, MaxPower is still 500 mA, but the phone charges at 300 mA. (http://codepad.org/eEXSBO76)

So: what's the culprit here? Is it possible my USB-C ports aren't delivering full power? How could I check?

Offline

#2 2020-09-16 14:16:52

sabroad
Member
Registered: 2015-05-24
Posts: 158

Re: USB-C port supplying low amount of power

spaetzle wrote:

Is it possible my USB-C ports aren't delivering full power? How could I check?

USB is confusing because it's actually a collection of protocols, extensible and optional. USB-C defines the connector and pins. USB-PD defines power negotiation between Source and Sink. Though USB-PD ports can support operation as both Source or Sink, this is not required. USB-PD Source requires complex protection circuitry.

For this reason, it's likely your USB-C ports support USB-PD Sink only. Thus, the BlackBerry is negotiating as a USB 3.1 SuperSpeed device and can request up to 900mA but be supplied by as little as 4V.

spaetzle wrote:

How could I check?

There are USB-PD sniffers from $50 but at that price you might as well just buy a $10 USB-PD charger.

For more on USB-PD than you care to know, see https://usb.org/sites/default/files/D2T … livery.pdf


--
saint_abroad

Offline

#3 2020-09-16 17:42:34

spaetzle
Member
From: Canada
Registered: 2020-09-16
Posts: 2

Re: USB-C port supplying low amount of power

sabroad wrote:

it's likely your USB-C ports support USB-PD Sink only

Sometimes when I plug the phone into the laptop via USB-C, it charges the laptop rather than vice versa. This only happens sporadically, and I haven't tested enough to figure out under what conditions, but it has happened with all three USB-C cables. If I then unplug and replug the phone, it usually switches the current flow back towards the phone.

That would seem to indicate both devices can serve as sink/source, no?

I guess what confuses me most is that the USB-A port serves a significantly higher charge than the USB-C port. Is that not unusual?

sabroad wrote:

USB is confusing because it's actually a collection of protocols, extensible and optional.

I was always vaguely aware that USB (and especially USB-C) was an absolute mess, but it's only while diving in to figure this out that I've realize how nuts it truly is.

Offline

#4 2020-09-16 21:58:33

sabroad
Member
Registered: 2015-05-24
Posts: 158

Re: USB-C port supplying low amount of power

spaetzle wrote:

I guess what confuses me most is that the USB-A port serves a significantly higher charge than the USB-C port. Is that not unusual?

There's also USB-BC which (apart from QC) enables ports to negotiate up to 5A (up from the 900mA of USB 3.0).

This isn't implemented with USB-C (as it can optionally negotiate 3A) which instead uses USB-PD (for power delivery, in practice).


--
saint_abroad

Offline

Board footer

Powered by FluxBB