I am going to use a micro-USB to power my MSP430 microcontroller. That means I only need the 5v and the GROUND pin. However, after discussing that the other pins should be untouched.. my friend said that was a bad idea. He said that I have to connect the D+ and D- to GND as well because I am not using them ? So my question is why should I connect them to GND ? and why should I use resistors to connect them to GND. Cant I just connect them to ground directly ? Shouldn't pins be named as NC here?
Here is a picture.
Best Answer
The USB D+ and D- lines are tied to resistors to establish a default state for the DEVICE (i.e. your MCU board in this case). Normally this connects to a HOST port that monitors the resistor connections to ascertain what type of port the DEVICE is (i.e. USB 1.1, USB 2.0 Full Speed or USB 2.0 High Speed). In the case where the connection is to a charger module or a high current capable charging port then the resistors may play a role of telling the charger that it can supply a higher power.
In fact some plug in chargers are designed by the manufacturer to only supply the higher charging current when the resistors on the D+ and/or D- are matching the ohms values that they put into their specific tablets/phones.
At least one universal charger manufacturer (ANKER) has chargers that can comprehend the various resistor sizes used and provide the full charging power accordingly.