Systems, methods and apparatus for wireless charging are disclosed. One method performed at a wireless charging device includes initiating transmission of a digital ping at a first power level a transmitting coil of the wireless charging device, increasing power level of the digital ping one or more times until current flowing to the transmitting coil has an amplitude that supports Amplitude Shift Key modulation of the digital ping, and determining a charging configuration for transferring power to a chargeable device when a response to the digital ping is received from the chargeable device.