Why Apple Couldn’t Go to Micro USB Charging

No feature of the new iPhone 5 has come in for as much criticism as Apple’s decision to drop the venerable 30-pin iPod connector in favor of a new, reversible 8-pin plug called Lightning.

Some people, especially those with a lot of iPod/iPhone/iPad accessories were understandably upset that they have suddenly been rendered obsolete. Photo of Lightning connectorThe $29 price for a Lightning-to-30-pin adapter doesn’t help, although that cost will undoubtedly come down as soon as third-party accessory makers bring theirs to market. The problem is that the nearly decade-0ld 30-pin was obsolete and too big, and was becoming a real design issue for Apple.

A more serious question is why Apple did not go to the micro USB connector that is supposed to be a standard in the phone industry. While the decision is surely due in part to Apple’s sense of esthetics and in part to Apple’s desire to control the accessory market through licensing of the proprietary Lightning connector, there was a truly compelling reason: The iPad.

Here’s the problem: The micro USB pins are very small, and the power-carrying connectors, pins 1 and 5, are rated to carry 1.8 amps at 5 volts DC. That means that the maximum charging power that can safely flow across the connector is 9 watts. But the iPad wants 10 watts to charge. It will charge on as little as 5 watts, the output of most USB 3 ports and the specially modified USB 2 ports on newer Apple products, but needs 10 watts for fastest charging.

Depending on the circuitry involved, there’s some danger that attempting to charge a USB iPad, if such a thing existed, would cause the connector to overheat. But the more likely result would be a 10% slowdown in the iPad’s charging rate, an especially unfortunate outcome on the already slow-charging third-generation device.

Apple has promised a micro USB-to-Lightning connector to comply with European Commission regulatory requirements. But I bet it will generate a warning regarding iPad use when the next generation of Lightning-equipped iPads appears.