Battery Management

The world has become increasingly more mobile. The functionalities of current notebooks are geared towards high mobility. This "luxury" has also become more and more important for specialized applications as well. Typical uses are, for example, patient monitoring in the medical field, different kinds of mobile measuring instruments, computers with special robustness that is required for harsh environments such as surveying or for use in automotive engineering for vehicle diagnosis where special functions are usually needed. Applications within these or similar fields require high flexibility and are therefore frequently created through the use of COMs (Computer On Modules), such as those based on the current XTX™ standard. The power supply system needed for these types of solutions should be easily implementable and highly flexible. For this reason congatec has developed an Embedded Battery Management concept that fulfills these requirements.

Battery management concepts found in notebooks, or other battery powered consumer products, rely on a closed, proprietary battery system. Due to this fixed setup there‘s no room for scalability, which was never intended for this type of application. This solution in turn results in high development costs that can only be justified for very large product quantities. This approach can‘t possibly fulfill the embedded application requirements for flexibility and short development times.

Embedded solutions can be rapidly developed using module concepts such as XTX™, ETX® or COM Express™. The battery management for such a solution must be designed to be extremely flexible because embedded applications have special requirements when considering mobile power supplies.

congatec is following the trend towards mobility by releasing the SBM² (SMART Battery Manager Module). It‘s an integrated module designed to provide a fast and risk free mobile battery solution. Additionally, the SBM² is only 68mm x 95mm and 12.5mm high. The only requirement is that the system‘s power supply provides 19V DC. The SBM² takes care of the rest. The input power limiter on the SBM² allows the dimensioning of the AC power supply to max. CPU power plus 25%. The SBM² distributes the current to the system and battery charger in an intelligent way. This results in reduced weight and costs when compared to a worst case scenario whereby dimensioning the power supply is necessary to provide maximum charge to the batteries and maximum power to the system in parallel.

congatec‘s SBM² SMART Battery Management Module can be easily integrated and provides a high measure of adaptability. SMART Batteries can be configured as 2S1P up to 4S3P. There is the possibility to use the batteries in either parallel or sequence. When using the sequential method, empty batteries can be exchanged with fresh ones. The parallel method uses both batteries simultaneously thereby enhancing the energy efficiency. This method can improve battery runtime up to 10%. Additionally the SBM² offers the possibility to control several LEDs, which provide the ability to view the load status of the battery. This feature can be helpful when the system operator wishes to visually check the load status of the battery without having to use the operating system.

The SBM² is equipped with its own microcontroller that communicates over the I²C bus with the board controller found on congatec CPU boards. The congatec board controller works closely together with the ACPI section of the congatec embedded BIOS. Communication to the operating system and the application itself is enabled through the use of the ACPI driver or the congatec CGOS API (a unified software interface for all congatec boards and common operating systems).

The communication data protocol between the SBM² and the congatec CPU board is based on the SBS-forum.org protocol. This protocol has been enhanced by congatec with a few additional functions but still remains fully backwards compatible. The address of the SMART battery system controller and the SMART battery itself has been merged into one microcontroller for the sole purpose of reducing system costs.

In order to provide a communication channel between the SBM² and the operating system, a „Control-Method-Batterie-Interface“ (CMB) was defined and implemented into the ACPI section of the congatec embedded BIOS. It offers the flexibility to interface with the battery system through a standardized software interface. With the help of this CMB interface, the operating system can efficiently control the behavior of the batteries by setting new battery-low trip points, or warning report thresholds, depending on the CPU load. ACPI compliant operating systems such as Microsoft Windows XP, Windows XP Embedded or LINUX can thereby directly access the status of the batteries and obtain information about the charge of the batteries, the current power source and the load status. When using other operating systems the software applications themselves can access the battery system using the congatec CGOS API. This API not only contains battery functions but also interfaces numerous different embedded functionalities that are available on congatec CPU boards. All common operating systems are supported by this uniform API.

In order to achieve long battery runtime, all modern computers are equipped with sophisticated power management modes. Apart from switching off the display and hard drive, the S3 power management mode offers additional energy savings. In S3, or suspend-to-RAM mode, the operating system saves the current system state in the main memory (RAM) and then switches the power supply to soft off. Once in this state the only voltage available is provided by the 5 volt standby line. The RAM uses this voltage for a self refresh. Suspend-to-RAM is supported by many congatec CPU boards as well as the SBM². Mobile solutions with high computing performance and long battery runtime are possible when utilizing these features.
For a quick evaluation of the SBM² SMART Battery Management Module congatec offers a starter kit that includes a SBM² module, a SMART Battery as well as a complete set of cables (picture 3) . This kit can be operated in conjunction with the congatec XTX™ starter kit. When used together they provide a fast and simple way of evaluating all the functionalities and configurations offered by the XTX™ and SBM² modules. If a customized systems is to be used then the SBM² can be easily attached to the customer specific baseboard. Optionally, it‘s possible to integrate the SBM² module into the baseboard design.

These modular concepts for computer functionality and battery management provide an excellent opportunity to individualize and customize embedded computer solutions. A single embedded system can become quite flexible in terms of performance by simply equipping it with different performance class CPU modules. By supporting a wide range of battery types and capacities the battery runtime can be scaled to the application requirements. Costs, reduced design risk, flexibility and development times can be optimized. All embedded PC applications that utilize batteries can profit from these modular concepts. (ce, May 8, 2006)