Specifications

Smart Battery Charger Specification
SBS Implementers Forum -Page 20- Revision 1.1
6.1.4. Charger Brown-Out Conditions
Situations may arise where the system attempts to charge a battery while the system is also being powered
from the AC power supply. In these cases, the charger may not draw so much power that the system’s
power source is compromised. The charger can, at its option, choose to charge the battery at a lower rate
automatically or abort charging entirely. The Smart Battery Charger will report when it lowers its output
by setting the ChargerStatus() register’s optional VOLTAGE_NOTREG and CURRENT_NOTREG bits as
appropriate.
6.1.5. Smart Battery Charger Leakage Current
A leakage current may flow between the Smart Battery and the Smart Battery Charger at times when no
current flow is expected (e.g. programmed zero charge current, Safety Signal value indicates no charging
allowed, no input power to the charger). Smart Battery Charger manufacturers are expected to minimize
leakage current to prevent unintended over-charging or unintended low-rate discharging which may result
in shortened battery life. Leakage currents should be less than 100uA.
6.1.6. “Float” Voltage
A Smart Battery Charger is allowed to output an arbitrary float voltage. The float voltage refers to the
voltage output of the charger with no battery connected. There may be a desire to design the system to
present a voltage on its terminals to minimize contact arcing when a battery is plugged in. When the
charger detects no battery present in the system, it may default to an output of 0 to its full-range voltage and
up to 10mA current.
6.1.7. Smart Battery Charger Start-Up
Upon start-up or at any other power-on condition (e.g., after POR_RESET has been set), the charger is
allowed to supply “wake-up” charge to the battery when the following conditions are satisfied: AC power
is present, a battery is present, the Safety Signal indicates that “wake-up” charging is allowed, and the
INHIBIT_CHARGE bit is not set. Once the time-out period expires, the charger can optionally continue to
“wake-up” charge only if the battery’s Safety Signal indicates that “wake-up” charging is allowed
indefinitely.
Battery packs may use a fixed resistor with a value less than 425 ohms for the Safety Signal to indicate that
they do not want the “wake-up” charge continued past the normal time-out period.
Some possible startup system scenarios:
• Constant current (e.g., NiMH) smart battery, intelligence “awake”, the battery:
• Sends both a ChargingCurrent() and ChargingVoltage() command to initiate charging.
• Sends a ChargingCurrent() or ChargingVoltage() or both to adjust the charging rate.
• When full, sends AlarmWarning() message, a POR_RESET, a zero ChargingCurrent() or zero
ChargingVoltage() to abort charging
• Constant current smart battery, intelligence “asleep”, the battery:
• Could take the “wake-up” period of charging to raise its voltage enough for the intelligence
to wake up or may expect wakeup charging to continue indefinitely as long as the Safety
Signal indicates that “wake-up” charging is allowed indefinitely.
• Constant voltage (e.g., Li-ion) smart battery, intelligence “awake”, the battery:
• Sends an AlarmWarning() message asking the charger to stop charging
• Sends ChargingCurrent() and ChargingVoltage() commands requesting constant voltage
charging.
• Constant voltage smart battery, intelligence “asleep” (also implies that a deep-discharge protection
FET is open-circuited as well)
• The voltage at the terminals of the battery pack should be enough to wake up the battery’s
microcontroller, which then sends charging voltage and current messages to the charger and
re-enables its protection device.