USB-C - can I ommit CC1/2 resistors 5k1 to gnd if I use it only for 5V charging? - Page 1
Forum section: electronics / projects

author: dusan
author_rank: Regular Contributor
timestamp: November 28, 2024, 07:23:06 am
content: I'm making lithium battery powered device with LTC4054 charger (charging current <500mA) and usb-c connector. I'm too tight on space. Can I ommit 5k1 resistors from CC1 and CC2 to ground?

author: ftg
author_rank: Frequent Contributor
timestamp: November 28, 2024, 07:57:42 am
content: Short answer: No.That will make USB-C chargers not work with it at all.Without the two 5k1 resistors only USB-A --> USB-C cables will work.A proper USB-C --> USB-C charger uses those resistors or USB-PD to determine what is at the end of the cable and if it wants any voltage.No resistors, no voltage.

author: SiliconWizard
author_rank: Super Contributor
timestamp: November 28, 2024, 08:48:33 am
content: As ftg said: no. Those resistors are the only way of making your device recognizable as a "sink" by any compliant USB-C source.Is space this tight that you could not fit even two 0201 resistors?

author: NiHaoMike
author_rank: Super Contributor
timestamp: November 28, 2024, 01:06:46 pm
content: That's a big cause of "cursed" USB-C devices on the market. Don't do it. As the old USB-A starts to get phased out, those cursed devices will stop working.I really think USB-C dropped the ball expecting the spec to be used by cheap devices. They should have defined shorting the CC lines to ground as a "dumb" device wanting 5V at 500mA or less. Any more and the resistors have to be used.

author: Siwastaja
author_rank: Super Contributor
timestamp: November 28, 2024, 01:12:09 pm
content: Quote from: NiHaoMike on November 28, 2024, 01:06:46 pmThen again, if a designer cannot follow this simple rule, they would also fail to connect the lines to ground. The problem probably is not about saving $0.0005 on resistors, it's about not reading the specifications, and a grounding requirement would get missed, too.

author: dusan
author_rank: Regular Contributor
timestamp: November 28, 2024, 03:09:55 pm
content: I switched to smaller resistor and found a space.

author: SiliconWizard
author_rank: Super Contributor
timestamp: November 28, 2024, 08:59:15 pm
content: Good. An alternative to the two resistors would be a PD controller - maybe you can find some very tiny ones in BGA packages that would have smaller footprint than two resistors, although with 0201, I doubt it.It would be more expensive, but more flexible.Note that some of those controllers do act as sinks by default and then can be reconfigured programmatically or via some pins.

author: bson
author_rank: Unknown
timestamp: November 28, 2024, 10:50:55 pm
content: Remember that with USB-C either side can provide power to the other. A device can power a laptop and a laptop can power a device. The resistors prevent both sides from trying to power Vbus at the same time. The pulldown requests power, and if it's not requested it can't be provided.

author: jbb
author_rank: Super Contributor
timestamp: November 28, 2024, 11:58:17 pm
content: Also please use separate resistors for CC1 and CC2. Tying CC1 and CC2 together in a device is forbidden and another way to make cursed devices.Case in point, my headphones have a USB C port and will charge just fine from a USB A -> C cord and the manufacturer provided USB C -> C cord but not an Apple USB C -> C cord.

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: November 29, 2024, 12:38:40 am
content: I've been buying quite a few random USBC powered gadgets from Aliexpress recently & about half of them don't have the resistors, so won't charge on a "proper" USBC supply. Fortunately quite a few actually have the footprints on the PCB, so they can be "fixed"

author: amyk
author_rank: Super Contributor
timestamp: November 29, 2024, 01:26:38 am
content: Quote from: Siwastaja on November 28, 2024, 01:12:09 pmIt's easier to not have to spend any extra effort for the simplest use case. I remember seeing dedicated USB-A charging receptacles that don't even have the data lines brought out, but they are connected together internally.USB-C is disgustingly overengineered complexity. I don't blame the implementers for missing the stupid little horrors of that design-by-committee mess.