Page 145 - Lindens Handbook of Batteries

5.22 PRINCIPLES OF OPERATION

As previously mentioned in the precharge example, other charge-gating information may also be
communicated relating to the specific conditions of the battery pack prior to initiation of charge.
During discharge, information from the battery to the end-equipment host device can be uti-
lized to maximize the run-time of the device while also preventing abusive discharge conditions.
In laptop computers, for example, various power management techniques are employed by the
notebook systems as the battery’s SOC decreases. High current loads, such as the spin-up current
from a hard disk or DVD player can be delayed briefly while the notebook reduces loads else-
where, perhaps momentarily dimming the screen backlight or powering down other subsections.
Advanced smart batteries can provide information to the notebook system so that such decisions
can be easily determined.
Gas-gauging that represents the run-time of the device in meaningful terms instead of SOC
percentages can also be communicated. Similar application-specific information that brings
more meaning to the end equipment and provides a more user-friendly experience is also pos-
sible. Smart batteries can provide information ranging from the time remaining during charge as
well as discharge, the number of usage cycles, and the approximate remaining useful life. In the
case of HEVs, the state-of-power is more valuable to the vehicle controller: can the battery sup-
port a high power load for enough time until the internal combustion engine can be restarted?
If not, then the engine may not be stopped until the battery has reached a higher state-of-power
capability.
In some devices, the reliability of the communication link is critical both to accurately
convey the data and to prevent unauthorized access. (Some battery systems include encryption
or challenge-response authentication to limit unauthorized battery packs to operate in the end-
equipment or charger.)

5.6.1 The Smart Battery System (SBS)
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A formalized electronic battery management system was created by leading cell suppliers, laptop
computer makers, and semiconductor manufacturers in 1995 to standardize the electrical interface
between battery packs, chargers, and notebook computers. This Smart Battery System (also called
SMBus System) has been widely adopted by notebook computer makers and other portable device
manufacturers for many industrial and general purpose battery systems. The physical form factor of
the battery packs is not standardized (although some standard sizes exist, such as the DR202). The
standardization is only for the communications interface.
The System Management Bus (SMBus) defines additional protocols and electrical requirements
on top of the I2C specification developed by Philips Corp. These protocols include error detecting
mechanisms, minimum voltage levels, and similar timing and power requirements. Typical portable
battery systems utilize SMBus V1.1, while fixed non-battery systems may also use SMBus V2.0 for
other devices, such as backlight controllers found in a typical notebook computer.
The Smart Battery System also includes specifications for the data content and transfer between a
host device such as a notebook computer, the smart battery, and a smart charger. The Smart Battery
Data Specification and the Smart Battery Charger Specification detail the interaction and data
requirements for each device. SBS smart batteries provide up to 34 data values, both measured and
calculated, that can be utilized by the host device or charger to enhance battery performance and
system power management. Similarly, there are three levels of smart chargers that can be utilized
in SBS platforms.
The goal of the smart battery interface is to provide adequate information for power management
and charge control regardless of the particular battery’s chemistry. The smart battery consists of a
collection of cells or single-cell batteries and is equipped with specialized hardware that provides
present state, calculated, and predicted information to the Host. The electronics need not be inside
the smart battery if the battery is not removable from the device.
Many semiconductor companies supply battery monitor, charger, or host controller products that
comply to the various SBS standards to provide easy operability. However, testing should still be done
with components since interpretation of the specifications has left some minor incompatibilities.