I have found that many USB wall chargers use a resistive voltage divider to set the D+ and D- pins to a specific voltage, usually between 2 and 3 volts. Other USB wall chargers short the D+ and D- pins together with no connection to anything else. From my experience some devices will not accept a charge rate above 500mA on the chargers using the voltage dividers, but will charge up to their max input on a charger with the data pins shorted. I have read things that suggest the opposite may be true as well, but have been unable to verify this. I am hoping to figure out which method provides the best compatibility with all USB devices.
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