BQ35100 Datasheet, PDF (17/26 Pages) Texas Instruments – Lithium Primary Battery Fuel Gauge

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bq35100
SLUSCM6A – JUNE 2016 – REVISED JULY 2016
Typical Applications (continued)
8.2.1 Design Requirements
For design guidelines, refer to the bq35100 EVM User's Guide (SLUUBH7).
8.2.2 Detailed Design Procedure
8.2.2.1 Gauging Mode Selection
The bq35100 can be used in any one of three different modes with the selection of the mode based on the
battery chemistry. The selection is made with the GMSEL[1:0] bits in Operation Config A.
The voltage correlation mode is typically used with Lithium Manganese Dioxide (LiMnO2) cells as the voltage vs.
state-of-health (SOH) profile has a defined slope to enable accuracy. The resistance correlation mode is only
used with Lithium Thionyl Chloride (LiSOCl2) cells.
The ACCUMULATOR mode (ACC) is chemistry-independent, but also provides no gas gauging data, such as
Remaining State-Of-Health, Full Charge Capacity, or End-Of-Service (EOS) indication. This is the default
configuration as it is also the required mode for the device when it is calibrated. Once calibration is completed,
the device can be set to the appropriate gauging mode.
8.2.2.2 Voltage Measurement Selection
The default configuration is for the bq35100 to support 1-series cell with a maximum of 4.5 V. If the battery
voltage can be above this level, then [EXTVCELL] in Operation Config A should be set. In this setting, an
external resistor divider is used to scale the voltage so the gauge can measure accurately.
8.2.2.3 Temperature Measurement Selection
There are three options for temperature measurement in the bq35100. By default, the device is configured to use
an external 103AT NTC thermistor. However, if [TEMPS] = 0, then an internal temperature sensor is used. This
requires no external components but for optimal performance in this case, the bq35100 should be very close to
the cell, preferably thermally connected.
There is one other option that can be used if the system already includes a cell temperature measurement
solution: If WRTEMP = 1, then the host can write the temperature to the device and the bq35100 algorithms will
use that data.
8.2.2.4 Current Sense Resistor Selection
The bq35100 calculates current through measuring a voltage across a small resistor in series with the battery.
The default value is 100 mΩ. To maximize current measurement accuracy, the ideal value is calculated as:
R_SENSE (mΩ) = V_(SR)Max / Peak Load Current (mA)
Where V_{(SR) MAX} = 125 mV
8.2.3 Expected Device Usage Profiles
The bq35100 is designed to work in a system where there is a period discharge pulse of at least 10 s of mA for
10 s of ms. In ACC mode, any pulse can be measured based on the information the host requires. However, in
EOS modes, the battery condition does not change very fast so only pulses that are many hours apart; for
example, 24 hours, are needed.
If the time between pulses needing monitoring is less than a minute, then it is recommended not to power down
the device. However, if the period is greater than 5 hours, then powering down the device between pulses is
expected. Periods in between risk not allowing the battery to rest and any EOS-related data may be
compromised. Battery EOS OCV BAD Warning provides more information on this.
The shorter the period between pulses has a large effect of the overall cumulative power consumption of the
battery electronics. See Device Functional Modes for more details on average power consumption.
Copyright © 2016, Texas Instruments Incorporated
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