Specifications

Smart Battery Charger Specification
SBS Implementers Forum -Page 31- Revision 1.1
No-host charging
Because the Smart Battery can communicate as a Master device on the SMBus, no Host device is required
for proper charging. Host electronics may be completely shut off and, as long as power is provided to
charge, the Smart Battery and Smart Battery Charger may communicate independent of the Host. This
functionality is especially beneficial in systems that do not have on-board charging capability or do not
require the system to be on for any other reason during charge.
System Host
Smart Battery
Charger
Smart Battery
Vbatt
Charging Voltage/Current Requests
SMBus
Critical Events
AC-DC
Converter
AC
Safety
Signal
No-Host Charging
(Unregulated)(Off or not present)
Master-only Host
Although SMBus is defined as a multiple-master bus, it is possible to operate SMBus components in
general and Smart Battery/Smart Battery Chargers in particular with a master-only Host. This
implementation may be necessary if a micro-controller is used as the System Host in addition to performing
other functions. Software complexity or multi-tasking may not permit a full multiple-master
implementation. In this case, a Master-only Host could be used if all other SMBus devices are Slave-only
or can be set to Slave-only.
If the system contains only the Host, Smart Battery and a Level 1 or 2 Smart Battery Charger, then the
Smart Battery is the only other Master device present. In this case, the Host must disable the automatic
broadcasts of the battery's ChargingVoltage() and ChargingCurrent() by setting Battery Mode
CHARGER_MODE bit. See the Smart Battery Data Specification for details (refer to the References
section). Once this is accomplished, the System Host is the only Master device for most operations. The
exception is the Smart Battery AlarmWarning() broadcast to the Smart Battery Charger and System Host.
This will be broadcast by the Smart Battery under some conditions (refer to the References section). It is
possible that a data collision will result making rebroadcast necessary. Because the System Host in this
case is Master-only and cannot receive this broadcast, it is necessary that the System Host occasionally poll
the Smart Battery for the AlarmWarning() status. It is also necessary that the System Host obey the SMBus
Specification requirement to check that the bus is idle before beginning a transaction as a master.
When using a Master-only Host, the Host must poll the Smart Battery for charging voltage and current, and
then transmit this data to the Smart Battery Charger. The Host should poll the Smart Battery for these
values at an interval of not less than 5 seconds nor greater than 1 minute in order to maintain correct
charging.