Resonant Qi and the iPhones

I previously did a really poor job of explaining the new iPhones’ wireless charging support, so I would like to rectify that. The new iPhones are Qi 1.2.3 devices, but the iPhone 8 currently only supports Qi 1.1.X. This means inductive-only charging, and no fast charging.

The resonant extension of the Qi standard was introduced with 1.2 in 2014, and compatible chargers have been available for years. Qi 1.2 also supports simultaneously charging multiple devices with optional WP-ID unique identifiers for power receivers.

The resonant specification allows for charging at greater distances (implementation-dependent) and does not require precise device-charger alignment. The medium power extension for 1.2 allows for charging above 5W using Extended Power Profile chargers, and the first devices came to market in 2016.

Apple is using Broadcom’s 2014 BCM59350 which only supports charging up to 7.5W. This limits the many resonant Qi chargers in the market that support up to 15W of power delivery. An upcoming iOS update will add support for Qi 1.2.3 and 7.5W (5V/1.5A) charging on an unknown date.

What I should have originally stated in my iPhone X article is that inductive charging is mostly useless, and resonant charging is only a little better at the moment. Far-field resonant charging will eventually provide a reasonable experience in the future. Of all the available options, Apple has chosen to bet on the future of the Qi specification.

 

Update

Here's a good explanation of resonant vs. inductive Qi.