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BQ76907
SLUSE96 – NOVEMBER 2023
the resolution such that the data exhibits 1-sigma variation with ±1-LSB) of the coulomb counter conversions
increases with longer timing between output data. The setting options when the coulomb counter is in full power
mode are 366 μs (which results in 13-bit effective resolution), 732 μs (14-bit effective resolution), 1.46 ms
(15-bit effective resolution), or 2.93 ms (16-bit effective resolution). This output rate is set using data memory
configuration bits. In addition, the coulomb counter supports a low power mode, which operates at a 16 times
slower rate than the settings listed above, with similar resolution performance at each setting, but drawing only 4
μA rather than ~60 μA at full power.
The CC1 filter generates a 16-bit current measurement that is used for charge integration and other decision
purposes, with one output generated every 250 ms when the device is operating in NORMAL mode and the
coulomb counter in full power mode, or one output every 4 seconds when the device is operating in low power
mode.
The integrated passed charge (from integration of the CC1 processed result) is available as a 48-bit value, which
includes the upper 16 bits of accumulated charge as the integer portion, the lower 32 bits of accumulated charge
as the fractional portion, and a 32-bit accumulated time over which the charge has been integrated in units of
seconds. The accumulated charge integration and timer can be reset by a command from the host over the
digital communications interface. Note that the charge and time are not integrated while in SLEEP mode.
See the
BQ76907 Technical Reference Manual
and their associated programmable settings.
7.5.3 Internal Temperature Measurement
The BQ76907 device integrates the capability to measure its internal die temperature by digitizing the difference
in internal transistor base-emitter voltages. This voltage is measured periodically as part of the measurement
loop and is processed to provide a reported temperature value available through the digital communications
interface.
The internal temperature is also compared to a programmable protection threshold to implement a die
overtemperature protection. In response to this protection, the device can be configured to disable FETs
and optionally enter SHUTDOWN mode. For more information on this, refer to the Internal Overtemperature
Protection section in the
7.5.4 Thermistor Temperature Measurement
The BQ76907 device supports measurement of an external thermistor on the TS pin. The device includes
an internal 20-kΩ pullup resistor to bias the thermistor during measurement. The TS pin can be selected for
thermistor measurement or general purpose ADCIN measurement using a data memory setting.
When the pin is selected for thermistor measurement, the internal pullup resistor is used to bias the pin during
the measurement. In order to provide a high precision result, the device uses the same 1.8-V internal LDO
voltage for the ADC reference as is used for biasing the thermistor pullup resistor, thereby implementing a
ratiometric measurement that removes the error contribution from the LDO voltage level. Because the pullup
resistor is only enabled during the pin measurement, it is recommended to limit the capacitance at this node to
reduce the effect of incomplete settling when the pullup resistor is biased. The capacitance is recommended to
stay below 4 nF when in highest resolution mode, or 500 pF when in highest speed mode.
If the pin is selected for general purpose ADCIN measurement, the pullup resistor is not enabled during
measurement, and the ADC uses VREF1 for its reference when measuring the pin.
The data is reported in units of 16-bit ADC counts. The fullscale digital value reflects an analog input level of
its reference × 5 / 3. So when the TS pin is measuring a thermistor in ratiometric mode using the 1.8-V internal
regulator for its reference, the 16-bit LSB is 1.8 V × 5 / 3 / 32768 ≅ 91.55 μV. When the TS pin is measuring in
ADCIN mode using the VREF1 reference, the 16-bit LSB is VREF1 × 5 / 3 / 32768 ≅ 61.80 μV.
7.5.5 Factory Trim and Calibration
The BQ76907 device includes factory trim for the cell voltage ADC measurements, the stack measurement, the
internal die temperature measurement, and the current measurements, in order to optimize the measurement
34
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BQ76907 Technical Reference
Product Folder Links:
for more details on current measurement, charge integration,
Manual.
BQ76907
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