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SLUUBH1C–August 2016–Revised March 2018
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Copyright © 2016–2018, Texas Instruments Incorporated
Battery Gauging
Chapter 5
SLUUBH1C–August 2016–Revised March 2018
Battery Gauging
The bq35100 device can operate in three distinct modes: ACCUMULATOR (ACC) mode, STATE-OF-
HEALTH (SOH) mode, and END-OF-SERVICE (EOS) mode. The device can be configured and used for
only one of these modes in the field, as it is not intended to be able to actively switch between modes
when in normal use.
5.1 ACCUMULATOR Mode
In this mode, the bq35100 device measures and updates cell voltage, cell temperature, and load current
every 1 s and begins accumulating after GAUGE_START is received. This data is provided through the
I
2
C interface while ControlStatus() [GA] is set.
This mode is enabled when [GMSEL1:0] in Operation Config A = 00.
5.1.1 Total Capacity Update
When in ACCUMULATOR mode, the bq35100 device tracks and then stores the total accumulated
capacity to its internal data flash.
CAUTION
Care should be taken when enabling and using this feature to ensure that the
maximum number of writes, which is 200,000, is not exceeded. For example,
this translates to no more than 25 writes per day over 20 years.
When the GE pin is asserted, the device will update AccumulatedCapacity() from the value stored in data
flash. When ControlStatus() [GA] is set, the device adds each coulomb counter measurement to the value
of AccumulatedCapacity().
Sending the GAUGE_STOP() command prior to the GE pin being pulled low initiates the latest value of
AccumulatedCapacity() to be written to data flash memory. As this operation takes a finite amount of time,
the gauge will assert [G_DONE] in ControlStatus() and can optionally trigger the ALERT pin to inform the
host when the operation is complete.
5.2 STATE-OF-HEALTH (SOH) Mode
This mode is enabled when [GMSEL1:0] in Operation Config A = 01. This mode is suitable for
determining SOH for Lithium Manganese Dioxide (LiMnO
2
) chemistry. In this mode, cell voltage and
temperature are precisely measured immediately after the GE pin is asserted. The gauge uses this data to
compute SOH.
SOH = DOD(TermV) – DOD(OCV, temperature)
Where:
TermV is a DF constant determined by the manufacturer to be discharge voltage below which the cell
cannot provide the power required by the device.
5.2.1 Low State-Of-Health Alert
BatteryStatus() [SOH_LOW] is set when StateOfHealth() is less than or equal to the value programmed in
SOHLOW for a period of SOH Set Time.
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