I'm looking for a part or app note that can determine how much current I can draw from the USB port that my device is plugged into. I have seen parts that do this, but they are dedicated Lithium Ion battery chargers. I have also seen parts that just determine what kind of port it is, but does not enumerate and determine what current can be drawn.
I do not need USB communication myself, just need to know the port power capabilities.
My application is charging a 3 series cell lithium battery. I have an MCU on board so an I2C or UART interface is fine. I'm not looking for a charging chip, just the USB current part.
I've seen the TPS251x, but that is for a host controller. Can I determine the max current of a USB port by just the data line voltages as a device, without enumerating? I've been reading that the only way to know between a low power 100mA and a high power 500mA port is to enumerate. Is that true?
USB C suppport is a plus.
I've also read about some devices determining a ports current by loading it until the voltage drops to some point. And adjusting the current continuously to maintain that voltage. So in case another device is plugged into the bus, it will cause a lower voltage drop and the device will lower it's current draw to compensate. Is this something common?
