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Architecture — An SMBus battery contains
permanent and temporary data. The permanent data is programmed
into the battery at the time of manufacturing and include
battery ID number, battery type, serial number, manufacturer’s
name and date of manufacture. The temporary data is acquired
during use and consists of cycle count, user pattern and maintenance
requirements. Some of the temporary data is being replaced
and renewed during the life of the battery.
The SMBus is divided into Level 1, 2 and
3. Level 1 has been eliminated because it does not provide
chemistry independent charging. Level 2 is designed for
in-circuit charging. A laptop that charges its battery within
the unit is a typical example of Level 2. Another application
of Level 2 is a battery that contains the charging circuit
within the pack. Level 3 is reserved for full-featured
external chargers.
Most external SMBus chargers are based on Level 3.
Unfortunately, this level is complex and the chargers are
costly to manufacture. Some lower cost chargers have emerged
that accommodate SMBus batteries but are not fully SBS compliant.
Manufacturers of SMBus batteries do not readily endorse this
shortcut. Safety is always a concern, but customers buy these
economy chargers because of the lower price.
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Figure 7-2:
Two-wire SMBus system.
The SMBus is based on a two-wire
system using a standardized communications protocol.
This system lends itself to standardized state-of-charge
and state-of-health measurements.
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Serious industrial battery users operating biomedical
instruments, data collection devices and survey equipment
use Level 3 chargers with full-fledged charge protocol.
No shortcuts are applied. To assure compatibility, the charger
and battery are matched and only approved packs are used.
The need to test and approve the marriage between specific
battery and charger types is unfortunate given that the ‘smart’
battery is intended to be universal.
Among the most popular SMBus batteries for portable
computers are the 35 and 202 form-factors. Manufactured
by Sony, Hitachi, GP Batteries, Moltech (formerly Energizer),
Moli Energy and many others, this battery works (should work)
in all portable equipment designed for this system.
Figure 7-3 illustrates the 35 and
202 series ‘smart' batteries. Although the ‘35’ has a
smaller footprint compared to the ‘202’, most chargers are
designed to accommodate all sizes, provided the common five-prong
knife connector is used.
Figure 7-3: 35
and 202 series ‘smart’ batteries featuring SMBus.
Available in NiCd, NiMH and
Li-ion chemistries, these batteries are used for mobile computing,
biomedical instruments and high-end survey equipment. The
same form factor also accommodates NiCd and NiMH chemistries
but without SMBus (‘dumb’).
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