Described herein is a wireless charging system including a wireless power transmitter and a wireless power receiver, where the wireless power receiver is part of a wireless electronic device such as a mobile telephone. The wireless power receiver is used to charge a battery of the wireless electronic device and can include both a closed-loop DC-DC converter, such as a buck charger, and an open-loop DC-DC converter, such as a switched capacitor charger. In addition to an in-band communication channel between the power transmitter and the power receiver, the system also includes an out-of-band communication channel through which the power transmitter and the power receiver can exchange control signals, helping to avoid interference that can occur in the in-band communication channel when using the open-loop DC-DC converter.