When charging my tablet using a bench supply, I notice that it only draws 0.45A, staying within the 0.5A limit. But the tablet is capable of charging at higher current. After researching on line, according to Battery Charging Specification, I found if the data lines were short to a resistance of 200 Ohms or less, it would be detected as a Charging Downstream Port, which supplies a minimum current of 1.5A. I connected a 130-Ohm between D+ and D-; the charging current now reaches 1.1A.
The tablet charging circuitry seems also to check the voltage and dials down the current if the voltage drops. When I set the supply voltage to 5V (the voltage at the tablet is less because of the drop on the wires), the current drops to 0.84A and 0.43A at 4.5V. It reaches max 1.13A at 5.2V.
