How does a 56k ohm resistor is a usb a to usb c cable function?

I understand that it is a there to protect the power delivery device from being asked to deliver a current greater then it was designed to. Could somebody explain how it works exactly. Does it limit the voltage/amperage to a specific ammount or is it part of a of negotiation system?

Why does samsung use a (usb a) to (usb c) cable and not just pure (usb c)?

Is it because adaptive fast charging operates at either 9v 1.67amps or 5v 2 amps? Does this fall in the 56k ohm resistor parameters? 


Is already asked this but I want to clarify a question. If I use a cable with a 56k ohm resistor with the adaptive fast charge block will it affect the charge speed?

4 Answers

  • 10 months ago

    Resistors negotiate the same way a brick wall does.

  • 10 months ago

    You won't get any usable power through a 56k resistor. Normally the resistor is connected between V- and one of the data pins to identify the connector as a charger, or between the 2 data pins to identify as a fast charger

  • 10 months ago

    USB charging ports (power outputs) either connect the data pins together, or use two resistor dividers across 5V to ground, which set a voltage on the data lines when there is no other signal present.

    (Or both - data pins connected and a resistor divider).

    Fast charge rated devices measure the voltages on the data pins to decide what type of USB port the cable is plugged in to, with what ratings.

    The 56K you mention can only be across one of the data lines to ground or power - if it were in series with anything, it would prevent either charging or data connections working.

    (With 5V, 56K would only allow a current of 5/56000 = 0.000089A; 89 microamps).

    It that resistor is connected in parallel with a resistor in the power source when the lead is plugged in, measuring how much the new voltage is would allow the device to determine the resistor values in the power unit, rather than just the voltage?

    That could be used to try and determine if it's a Samsung charger or a copy?

    Samsung are very picky with the cable and power specs as it is, I can believe they add more checks.

    Examples of some common USB power unit resistor configurations:

    And a much longer list with more info towards the bottom of this page:

    [The photo yahoo has put in below is from the first link].

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