Multiple digitized current values are available for readout over the serial communications interface, including two
using separate hardware digital filters, CC1 and CC2, as well as a firmware filter CC3.
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.
The CC2 filter generates a 24-bit current measurement that is used for current reporting, with one output every
3 ms when the device is operating in NORMAL mode (which can be reduced to one output every 1.5 ms based
on setting, with reduced measurement resolution). It is reported in 16-bit format, and the 24-bit CC2 data is also
available as raw coulomb counter ADC counts, provided in 32-bit format (with the data contained in the lower 24
bits and the upper 8 bits sign-extended).
The CC3 filter output is an average of a programmable number of CC2 current samples (up to 255), based on
configuration setting. The CC3 output is reported in 32-bit format.
The integrated passed charge is available as a 64-bit value, which includes the upper 32 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.
10.4 Synchronized Voltage and Current Measurement
While the cell voltages are digitized sequentially using a single muxed ADC during normal operation, the current
is digitized continuously by the dedicated coulomb counter ADC. The current is measured synchronously with
each cell voltage measurement, and can be used for individual cell impedance analysis. The ongoing periodic
current measurements can be read out through the digital communication interface, while the measurements
taken that were synchronized with particular cell voltage measurements are stored paired with the associated
cell voltage measurement for separate readout. These values can be read using a block subcommand, which
ensures the synchronously aligned voltage and current data are read out together.
10.5 Internal Temperature Measurement
The BQ76942 device integrates the capability to measure its internal die temperature by digitizing the difference
in internal transistor base-emitter voltages (deltaV
BE
). 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. This internal temperature measurement can be used for cell or FET temperature
protections and logic based on configuration settings.
10.6 Thermistor Temperature Measurement
The BQ76942 device includes an on-chip temperature measurement and can support up to nine external
thermistors on multifunction pins (TS1, TS2, TS3, CFETOFF, DFETOFF, ALERT, HDQ, DCHG, and DDSG). The
device includes an internal pullup resistor to bias a thermistor during measurement.
The internal pullup resistor has two options that can set the pullup resistor to either 18-kΩ or 180-kΩ (or none
at all). The 18-kΩ option is intended for use with thermistors such as the Semitec 103-AT, which has 10-kΩ
resistance at room temperature. The 180-kΩ option is intended for use with higher resistance thermistors such
as the Semitec 204AP-2, which has 200-kΩ resistance at room temperature. The resistor values are measured
during factory production and stored within the device for use during temperature calculation. The individual pin
configuration registers determine which pin is used for a thermistor measurement, what value of pullup resistor is
used, as well as whether the thermistor measurement is used for a cell or FET temperature reading.
SLUSE14B – DECEMBER 2020 – REVISED DECEMBER 2021
Copyright © 2021 Texas Instruments Incorporated
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