The device includes a factory gain trim for the voltage measurements performed using the general purpose ADC
input capability on the multifunction pins as well as the TS1, TS2, and TS3 pins. It also includes factory gain trim
on the voltage measurements of the PACK pin, the LD pin, and the top-of-stack (VC14) pin.
10.8 Voltage Calibration (ADC Measurements)
The BQ769142 device includes an optional capability for the customer to calibrate each cell voltage gain and the
gain for the stack voltage, the PACK pin voltage, and the LD pin voltage individually, and multifunction pin
general ADC measurements. An offset calibration value
Calibration:Vcell Offset:Vcell Offset
is included for
use with the cell voltage measurements, and
Calibration:Vdiv Offset:Vdiv Offset
is used with the TOS (stack),
PACK, and LD voltage measurements. The cell voltage gains determined during calibration are written in
Calibration:Voltage:Cell 1 Gain – Cell 14 Gain
, where
Cell 1 Gain
is used for the measurement of VC1–VC0,
Cell 2 Gain
is used for the measurement of VC2–VC1, and so forth. Similarly, the calibration voltage gain for the
TOS voltage should be written in
Calibration:Voltage:TOS Gain
, the PACK pin voltage gain in
Calibration:Voltage:Pack Gain
, the LD pin voltage gain in
Calibration:Voltage:LD Gain
, and multifunction pin
general purpose ADCIN measurement gain in
Calibration:Voltage:ADC Gain
.
If values for the calibration gain configuration are not written, the BQ769142 device uses a factory trim or default
values for the respective gain values. When a calibration gain configuration value is written, the device will use
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 will read back either with all zeros, if they
have not been overwritten, or whatever values have been written to these registers. Upon exiting
CONFIG_UPDATE mode, readback of the Cell Gain parameters will provide the values presently used in
operation.
Further details on calibration procedures can be found in the
BQ769142 Technical Reference Manual
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
. Using a value for VREF1 of 1.25 V, the nominal gain
for the cell measurements is 12409, while the nominal gain for the ADCIN measurements is 4166. 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()
,
LD Pin Voltage()
), and
Calibration:Vdiv Offset:Vdiv Offset
all
have units of userV.
10.9 Voltage Calibration (COV and CUV Protections)
The BQ769142 device includes optional capabilities for the customer to calibrate the COV (cell overvoltage) and
CUV (cell undervoltage) protection thresholds on the production line to improve threshold accuracy in the
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 VC14 and VC13A that is equal to the desired COV threshold. Next, the
host sends the
CAL_COV()
subcommand, which causes the BQ769142 device to perform a search for the
SLUSE91A – SEPTEMBER 2020 – REVISED FEBRUARY 2021
38
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