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SLUUBH1C–August 2016–Revised March 2018
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Copyright © 2016–2018, Texas Instruments Incorporated
Basic Measurement Systems
Chapter 2
SLUUBH1C–August 2016–Revised March 2018
Basic Measurement Systems
2.1 Voltage
The bq35100 device measures the BAT input using the integrated delta-sigma ADC, which is scaled by
the internal translation network, through the ADC. The measured voltage is available through Voltage(),
and is updated for the host to read once per second. The translation gain function is determined by a
calibration process. See Factory Calibration for further details.
In systems where the battery voltage is greater than V
IN(BAT)
MAX (for example, 2-series cell or more), an
external voltage scaling circuit is required. If [EXTVCELL] is set, then the voltage is measured via the VIN
pin. The input to VIN must be scaled to a maximum of 1 V.
The VEN pin can be used to enable and disable the external divider to conserve power. The firmware will
then scale this < 1-V value to reflect an average cell value, and then again by the number of series cells to
reflect the full battery voltage value.
CLASS SUBCLASS NAME TYPE SIZE MIN VALUE
MAX
VALUE
DEFAULT
VALUE
UNIT
Gas gauging Design
Series cell
count
Integer 1 1 8 1 Count
The configured battery voltage measurement is made available through the Voltage() command.
2.2 Temperature
The device can measure temperature through an integrated temperature sensor or an external NTC
thermistor using the integrated delta-sigma ADC. Only one source can be used for gauging and the
selection is made by setting Operation A [TEMPS] appropriately. The resulting measured temperature is
available through the Temperature() command, and is updated for the host to read once per second. The
internal temperature sensor is always measured in support of voltage measurement accuracy, and the
result is also available through the InternalTemperature() command.
When an external thermistor is used, REG25 (pin 7) is used to bias the thermistor, and TS (pin 11) is used
to measure the thermistor voltage (a pull-down circuit is implemented inside the device). The device then
correlates the voltage to temperature, assuming the thermistor is a Semitec 103AT or similar device.
There is a configurable option for the host to write the temperature to the Temperature() command when
[WRTEMP] = 1. This option is disabled by default.
2.3 Coulombs
The integrating delta-sigma ADC (coulomb counter) 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 in a range 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. This measurement is updated for the host to read
once per second.
2.4 Current
For the primary battery current, the integrating 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, and is updated for the host to read once
per second.
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