# Is it sufficient to put 5.1k pulldowns on CC1 and CC2 of USBC to get 5V 1.5A?

My device needs 1.5A at 5V from a USBC connector. I already have 5.1k resistors in place on both CC1 and CC2 and a fuse rated for 1.5A. However, I have read on here in another thread that apparently some USBC supplies do limit the current to 500mA when the UFP does not actually negotiate. Is this true? Is there a way I could perhaps tie D+ and D- to always get the maximum the supply can output?

The reason I am asking this is that I also measure the voltage on CC1 and CC2 and will adapt the consumption, but if the DFP's pull-ups tell me it's capable of 1.5A but it still limits the supply to 500mA, my device won't know it and will run out of juice.

With USB C, you have to follow the negotiation rules.

• After attaching, you are allowed to pull 100mA

• If you detect the USB 3.0 pins are active, you have 150ma.

If you need more current, you have the following things you can do:

• Talk over USB 2.0, requesting more power units. You can get up to 500ma@5V using this way
• Talk over USB 3.0, requesting more power units, you can get up to 750ma@5V using this way
• Talk over the USB data wires with proprietary charger standard, like Quick-charge or Apple
• Read the voltage on CC1, if it is above 0.7V, you can draw 1.5A @5V (see USB Type-C Spec R2.0 - August 2019 page 241)
• Read the voltage on CC2, if it is above 0.7V, you can draw 1.5A @5V (see USB Type-C Spec R2.0 - August 2019 page 241)
• Read the voltage on CC1, if it is above 1.31V, you can draw 3A @5V (see USB Type-C Spec R2.0 - August 2019 page 241)
• Read the voltage on CC2, if it is above 1.31V, you can draw 3A @5V (see USB Type-C Spec R2.0 - August 2019 page 241)
• Communicate with the charger with active USB PD. (over either CC1 or CC2) You can get up to the chargers limit of 5A@48V

Note that the standard says any USB C source on a multiport charger should at least support 1.5A @ 5V (page 228)

If the user connects you device with an A to C legacy cable, only the first few options are available to see if you can get more current

• Thanks for your answer, I like the summary approach. Two questions: 1) Are you sure it's sufficient to check only CC1 or only CC2? Your wording seems to imply this whereas I thought that the current levels allowed came from the combination of the voltages on these pins. 2) If a A to C cable is used, but only plugged in a wall charger and not a computer USB port, does that give at least 500mA? Nov 21, 2022 at 16:08
• 1: you have to check both CC1 and CC2, both pins have their own resistor, and one can be 0V (connected to the <1k resistor in the active cable), while the other one is connected to the other side. 2: with an USB A to C cable, you are supposed to follow these rules, but allmost all sources allow devices to draw 500mA without the proper negotiation steps in the real world Nov 21, 2022 at 19:50

This is how I interpret it: Both the source and the device must be capable of 1.5A with usb-c. This means both ends must be USB-C. So the source must have Rp resistors of 22k and the device can have 5.1k resistors and both ends must be C type connectors (A to C won't work)

• Thanks for the answer. So do you mean that as long as I have those 5.1k pull downs, and that the charger is a proper USBC device, I should get 1.5A ? Does that mean that the chargers I've heard about were not implementing the standard correctly? Nov 18, 2022 at 18:08
• Yes, summer if the chargers don't implement the standard properly. The charger has to have a controller on it, sometimes they cheap out and just do a voltage rail Nov 19, 2022 at 2:01