BQ35100 Datasheet, PDF (10/26 Pages) Texas Instruments – Lithium Primary Battery Fuel Gauge

bq35100
SLUSCM6A – JUNE 2016 – REVISED JULY 2016
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Feature Description (continued)
7.3.1.3 Coulombs
The integrating delta-sigma ADC in the device measures the discharge flow of the battery by measuring the
voltage drop across a small-value sense resistor between the SRP and SRN pins.
The 15-bit integrating ADC measures bipolar signals from –0.125 V to 0.125 V. The device continuously monitors
the measured current and integrates this value over time using an internal counter.
7.3.1.4 Current
For the primary battery current, the standard delta-sigma ADC in the device measures the discharge current of
the battery by measuring the voltage drop across a small-value sense resistor between the SRP and SRN pins,
and is available through the Current() command.
The measured current also includes the current consumed by the device. To subtract this value from the reported
current, a value programmed in EOS Gauge Load Current is subtracted for improved accuracy.
7.3.2 Battery Gauging
The bq35100 can operate in three distinct modes: ACCUMULATOR (ACC) mode, STATE-OF-HEALTH (SOH)
mode, and END-OF-SERVICE mode (EOS). 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.
7.3.2.1 ACCUMULATOR Mode (ACC)
In this mode, the bq35100 measures and updates cell voltage, cell temperature, and load current every 1 s. This
data is provided through the I²C interface while ControlStatus() [GA] is set.
7.3.2.2 STATE-OF-HEALTH (SOH) Mode
This mode is suitable for determining SOH for Lithium Manganese Dioxide (LiMnO2) 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.
7.3.2.2.1 Low State-of-Health Alert
BatteryStatus() [SOH_LOW] is set when StateOfCharge() is less than or equal to the value programmed in
SOHLOW.
7.3.2.3 END-OF-SERVICE (EOS) Mode
This mode is suitable for gauging Lithium Thionyl Chloride (LiSOCl2) cells. The End-Of-Service (EOS) gauging
algorithm uses voltage, current, and temperature data to determine the resistance (R) and rate of change of
resistance of the battery. The resistance data is then used to find Depth of Discharge (DOD) = DOD(R). As
above, SOH is determined and in turn used to determine the EOS condition.
7.3.2.3.1 Initial EOS Learning
For optimal accuracy, the first event where the device updates its impedance value is required to be when the
battery is full (a fresh battery). If the battery has been partially discharged, then the accuracy of the EOS
detection will be compromised.
When a new battery is inserted, then the NEW_BATTERY() command should be sent to the device to ensure the
initial learned resistance RNEW is refreshed correctly.
7.3.2.3.1.1 End-Of-Service Detection
The bq35100 can detect when a sharp increase in the trend of tracked impedance occurs, indicating that the
battery is reaching its EOS condition.
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