The convenience of the unbridled world of mobile phones, personal wearables and the many wireless sensors and controllers in our homes comes at a price: the constant attention and management of the rechargeable batteries that power them.
Recent proposals have been made to provide alternative ways of keeping them running, such as supercapacitors, energy harvesting from radio waves and vibrational energy from the surrounding environment. But these alternatives alone are not enough. To ensure a stable power supply, rechargeable batteries (currently based on lithium-ion batteries) will be necessary.
As we have relied on rechargeable batteries for over a decade, I have been puzzled that a common device and protocol independent standard has not yet emerged.
Until relatively rechargeable battery management has been a quasi-system. Typical low-cost relatively clunky battery solutions usually consisted of only identification resistors connected to the battery pack terminals. Alternatively, the battery pack may include a resistive temperature sensor next to the power connector. The measured value of the pull-down resistor indicates capacity and chemical information.
There are many so-called intelligent battery management solutions available. But they are either company, industry or application specific, although they all use the same battery type, size and chemistry. This problem will only get worse as we move from a world of nearly 8 billion mobile phone users to a world where there will be tens, if not hundreds, of billions of battery-dependent wearable wireless IoT devices. This does not include existing consumer products that require reliable battery management.
My candidate for standard cross-platform battery management is the Battery Interface (BIF) specification developed by the MIPI Alliance. 250 company members of MIPI originally positioned BIF for mobile phones and computing devices. While it has taken longer than I expected for it to become widely used in mobile devices, I have no doubt that BIF will dominate not only there, but more broadly. There are two reasons for my optimism.
One is that the MIPI Alliance's BIF working group has not attempted to cover all aspects of rechargeable battery management. Instead, it has limited its focus to how the battery subsystem communicates with the other devices in which it resides (currently mobile phones).
But because it only deals with the hardware and software aspects of the communication interface, rather than being particularly device-specific, it looks like an ideal choice for power-constrained wireless platforms such as wearables and other consumer IoT devices. And because it doesn't try to do more than is necessary (a problem with many industry standards) BIF offers the promise of being suitable for battery chemistries other than the lithium-ion batteries currently used in mobile phones and other wireless devices.
In terms of hardware, the BIF is as minimalist as possible, with hardware transceivers that can be implemented in gates as small as 1k using typical non-frontier CMOS processes. This is small enough to be easily integrated into a mobile phone power management IC (PMIC) or digital baseband IC (BB).
While its small gate count would make it an excellent candidate for IoT and wearable devices, it is in its favour that the specification only adds one line to the two existing power connectors VBAT and GND, the Battery Communication Line (BCL), in a typical mobile phone. With a single BCL line, the BIF communication protocol is intended to provide all the signals needed for a range of management functions: battery presence detection, analogue battery identification, and data, address and command words, in-band interrupts, and power save wake up commands.
The second reason why I think BIF can establish itself more widely is the software management scheme proposed by the working group. In order to manage all the functions sent over a pin connection, they defined an algorithm that allows developers to define a set of battery charging rules that can be stored in no more than 64k bytes of addressable RAM, ROM or reprogrammable non-volatile memory for each slave device in the system. In addition to some generic software drivers, the scheme allows developers to include functionality for host charging control in a rule-based algorithm, stored in a priority order specific to the application requirements.
However, even with such a scheme available, there are many low cost 'dummy' analogue batteries to consider and identify. the BIF working group has taken this into account by connecting a pull down resistor between BCL and GND, allowing the BIF based battery subsystem to identify whether the battery is a smart or low cost type and to determine the electrical characteristics. Low cost batteries.
