importance of full smart battery data (SBData) specification implementation: Part II, The

Advanced Battery Technology, Sep 1999 by Friel, Dan

Part I appeared in the August ABT.

Time Remaining

The time remaining at present and predicted rates are calculated using the previously discussed capacity information and the Smart Battery's ability to predict when the capacity will be depleted, based on both measurements and knowledge of the battery cell's performance. These data values are:

RunTimeToEmpty (minutes)

AverageTimeToEmpty (minutes)

AverageTimeToFull (minutes)

AtRate (mA or 10mW)

AtRateTimeToFull (minutes)

AtRateTimeToEmpty (minutes)

AtRateOK (Boolean flag)

These time-remaining functions are also impacted by the CAPACITY-MODE control flag in the BatteryMode data function. Only the AtRate function is explicitly affected since the value written to AtRate may be in either mA or 10mW depending on the mode. The other calculated time-remaining values may be affected due to alterations in how the capacity values are calculated based on the CAPACITYMODE setting.

Values written to AtRate are not assumed to be automatically converted if the CAPACITY-MODE flag is altered in BatteryMode. Therefore, before using the AtRate time functions, the original value in AtRate should be confirmed along with the present CAPACITY-MODE setting.

Granularity on all time values is set to two minutes although better performance is suggested. Accuracy values are dependent on the MaxError value and should represent minimum "safe" and conservative times.

Alarms and Broadcasts

The ability of the Smart Battery to respond even when not being addressed is critical to the safe and reliable operation of the complete system. Additionally, the ability to instruct a Smart Charger how to control charging voltage and current also contributes to system safety and ease of use. The broadcast data values are:

AlarmWarning (bit flags)

RemainingCapacityAlarm (mAH or 10mWH)

RemainingTimeAlarm (minutes)

ChargingCurrent (mA)

ChargingVoltage (mV)

The alarm functions in AlarmWarning is identical to the BatteryStatus data value except for the lowermost four bits of Alarm Warning which default to high. These bits represent the most recent error code when read from the BatteryStatus data function. The remaining upper bits are identical in both functions.

The minimum and maximum rates of broadcasting are defined to insure safety in charging situations. Alarm broadcasts have higher rates than charging instruction broadcasts. Termination warnings may also be broadcast to multiple sources (not simply the Smart Charger, for example) to provide an additional safety notification method. In all cases, the Smart Battery may not broadcast at all during the first 10 seconds of an initialized SMBus (both lines go high).

The RemainingCapacityAlarm must permit set points represented in either mAH or 10mWH as determined by the CAPACITY-MODE control bit in the BatteryMode data function. Initial (at time of first use after manufacture) values for RemainingCapacityAlarm must be 10% of DesignCapacity and the RemainingTimeAlarm must be 10 minutes.

Both settable alarms (RemainingTimeAlarm and RemainingCapacityAlarm) must support the zero set point to allow the alarm to be disabled if desired. All other alarm functions may NOT be disabled.

The charging broadcasts of ChargingCurrent and ChargingVoltage may be disabled by the CHARGERMODE control bit in the BatteryStatus function. However, when a Smart Battery is disconnected from the SMBus system (bus lines both low for more than two (2) seconds), the default state of CHARGERMODE = 0 (broadcasts NOT disabled) must be restored.

Mode, Status, and Errors

Understanding the operational parameters and error conditions of the Smart Battery is key to maintaining a reliable system, particularly when more than one device may be involved. The Smart Battery can provide additional system information through use of the mode, status and error functions:

BatteryMode

CAPACITY-MODE

CHARGER-MODE

MaxError

BatteryStatus

ManufacturerAccess

The required control flags in the BatteryMode data function are listed above. The following control flags are NOT required from BatteryMode but may be used to provide additional system information. The sub-control flags shown must be supported if the "enabled" or "support" portion is available:

CHARGE-CONTROLLER-ENABLED

INTERNAL-CHARGE-CONTROLLER

PRIMARY-BATTERY-SUPPORT

PRIMARY-BATTERY

Default conditions require that the following BatteryMode control bits be cleared when a Smart Battery is disconnected from a SMBus system, both lines low for more than two (2) seconds:

CAPACITY-MODE

CHARGER-MODE

CHARGE-CONTROLLER-ENABLED (if available)

PRIMARY-BATTERY (if available)

These defaults insure that a battery inserted into a system has a defined mode of operation.

Historical and Identification

Background information and identification of the Smart Battery can be used when multiple battery systems are employed and when battery life has dropped to a point of poor performance. Historical information can then be used by the system to determine the best moment to replace the Smart Battery for a fresh one.

The data values are: