Texas Instruments BQ76942, Руководство пользователя

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If values for the calibration gain configuration are not written, the BQ76942 device uses factory trim or default
values for the respective gain values. When a calibration gain configuration value is written, the device uses that
in place of any factory trim or default gain. The raw ADC measurement data (in units of counts) is corrected
by first subtracting a stored offset trim value, then the gain is applied, then the
Calibration:Vcell Offset:Vcell
Offset (for cell voltage measurements) or the Calibration:Vdiv Offset:Vdiv Offset (for TOS, PACK, or LD
voltage measurements) is subtracted before the final voltage value is reported.
The factory trim values for the Cell Gain parameters can be read from the Cell Gain data memory registers
while in FULLACCESS mode but not in CONFIG_UPDATE mode, if the data memory values have not been
overwritten. While in CONFIG_UPDATE mode, the Cell Gain values read back either all zeros, if they have not
been overwritten, or the values written to these registers. Upon exiting CONFIG_UPDATE mode, readback of
the Cell Gain parameters provides the values presently used in operation.
See the BQ76942 Technical Reference Manual for further details.
The effective fullscale digital range of the cell measurement is 5 × VREF1, and the effective fullscale digital
range of the ADCIN measurement is 1.667 × VREF1, although the voltages applied for these measurements
should be limited based on the specifications in
Specifications . Using a value for VREF1 of 1.212 V, the nominal
gain for the cell measurements is 12120, while the nominal gain for the ADCIN measurements is 4040. The
reported voltages are calculated as:
Cell # Voltage() = Calibration:Voltage:Cell # Gain × (16-bit ADC counts) / 65536 – Calibration:Vcell Offset:Vcell Offset
Stack Voltage() = Calibration:Voltage:TOS Gain × (16-bit ADC counts) / 65536 – Calibration:Vdiv Offset:Vdiv Offset
PACK Pin Voltage() = Calibration:Voltage:Pack Gain × (16-bit ADC counts) / 65536 – Calibration:Vdiv Offset:Vdiv Offset
LD Pin Voltage() = Calibration:Voltage:LD Gain × (16-bit ADC counts) / 65536 – Calibration:Vdiv Offset:Vdiv Offset
ADCIN Voltage = Calibration:Voltage:ADC Gain × (16-bit ADC counts) / 65536
Note
Cell # Voltage() and Calibration:Vcell Offset:Vcell Offset have units of mV. The divider voltages
( Stack Voltage() , PACK Pin Voltage() , and LD Pin Voltage() ) and Calibration:Vdiv Offset:Vdiv Offset
have units of userV.
10.9 Voltage Calibration (COV and CUV Protections)
The BQ76942 device includes optional capability for the customer to calibrate the COV (cell overvoltage) and
CUV (cell undervoltage) protection thresholds on the production line, in order to improve threshold accuracy in
system or to realize a threshold between the preset thresholds available from the device.
This calibration is performed while the device is in CONFIG_UPDATE mode. To calibrate the COV threshold,
an external voltage is first applied between VC10 and VC9 that is equal to the desired COV threshold. Next,
the
CAL_COV() subcommand is sent by the host, which causes the BQ76942 device to perform a search for
the appropriate calibration coefficients to realize a COV threshold at or close to the applied voltage level. When
this search is completed, the resulting calibration coefficient is returned by the subcommand and automatically
written into the
Protections:COV:COV Threshold Override configuration parameter. If this parameter is
nonzero, the device will not use its factory trim settings but will instead use this value.
The CUV threshold is calibrated similarly, an external voltage is applied between VC10 and VC9 equal to the
desired CUV threshold. Next, while in CONFIG_UPDATE mode, the
CAL_CUV() subcommand is sent by the
host, which causes the BQ76942 device to perform a search for the appropriate calibration coefficients to realize
a CUV threshold at or close to the applied voltage level. When this search is completed, the resulting calibration
coefficient is returned by the subcommand and automatically written into the
Protections:CUV:CUV Threshold
Override configuration parameter.
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BQ76942
SLUSE14B – DECEMBER 2020 – REVISED DECEMBER 2021
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