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Measurements taken using Semitec 103-AT thermistor, default temperature polynomial, and 18-kΩ internal pullup resistor.
16.2.4 Calibration Process
The BQ769142 device enables customers to calibrate the current, voltage, and temperature measurements on
the customer production line. Detailed procedures are included in the BQ769142 Technical Reference Manual
(SLUUCF2). The device provides the capability to calibrate individual cell voltage measurements, stack voltage,
PACK pin voltage, LD pin voltage, current measurement, and individual temperature measurements.
16.3 Random Cell Connection Support
The BQ769142 device supports a random connection sequence of cells to the device during pack
manufacturing. For example, cell-10 in a 14-cell stack might be first connected at the input terminals leading to
pins VC10 and VC9, then cell-4 may next be connected at the input terminals leading to pins VC4 and VC3, and
so on. It is not necessary to connect the negative terminal of cell-1 first at VC0. As another example, consider a
cell stack that is already assembled and cells already interconnected to each other, then the stack is connected
to the PCB through a connector, which is plugged or soldered to the PCB. In this case, the sequence order in
which the connections are made to the PCB can be random in time, they do not need to be controlled in a
certain sequence.
There are, however, some restrictions to how the cells are connected during manufacturing:
•
To avoid misunderstanding, note that the cells in a stack cannot be randomly connected to any VC pin on
the device, such as the lowest cell (cell-1) connected to VC13A, while the top cell (cell-14) is connected to
VC4, and so on. It is important that the cells in the stack be connected in ascending pin order, with the lowest
cell (cell-1) connected between VC1 and VC0, the next higher voltage cell (cell-2) connected between VC2
and VC1, and so on.
•
The random cell connection support is possible due to high voltage tolerance on pins VC1–VC14.
VC0 has a lower voltage tolerance. This is because VC0 should be connected through the series-
cell input resistor to the VSS pin on the PCB, before any cells are attached to the PCB. Thus, the
VC0 pin voltage is expected to remain close to the VSS pin voltage during cell attach. If VC0 is not
connected through the series resistor to VSS on the PCB, then cells cannot be connected in
random sequence.
•
Each of the VC1–VC14 pins includes a diode between the pin and the adjacent lower cell input pin (that is,
between VC14 and VC13A, between VC9 and VC8, and so on), which is reverse biased in normal operation.
This means an upper cell input pin should not be driven to a low voltage while a lower cell input pin is driven
to a higher voltage, since this would forward bias these diodes. During cell attach, the cell input terminals
Copyright © 2021 Texas Instruments Incorporated
Figure 16-4. Thermistor Temperature Error
Note
Product Folder Links:
SLUSE91A – SEPTEMBER 2020 – REVISED FEBRUARY 2021
BQ769142
BQ769142
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