When used as digital outputs, the pins can be configured to drive an active high output, with the output voltage
driven from either the REG18 1.8-V LDO or the REG1 LDO (which can be programmed from 1.8 V to 5.0 V).
Note
If a DC or significant transient current can be driven by a pin, then the output should be configured to
drive using the REG1 LDO, not the REG18 LDO.
When the pins are configured for DDSG and DCHG functionality, they provide signals related to protection faults
that (on the DCHG pin) would normally cause the CHG driver to be disabled or (on the DDSG pin) would
normally cause the DSG driver to be disabled. These signals can be used to control external protection circuitry,
if the integrated high-side NFET drivers will not be used in the system. They can also be used as interrupts in
manual FET control mode for the host processor to decide whether to disable the FETs through commands or
using the CFETOFF and DFETOFF pins.
12.10 Fuse Drive
The FUSE pin on the BQ76942 device can be used to blow a chemical fuse in the presence of a permanent fail
(PF), as well as to detect if an external secondary protector in the system has detected a fault and is attempting
to blow the fuse itself. The pin is intended to drive the gate of an NFET, which can be combined with the drive
from an external secondary protector, as shown in
. When the FUSE pin is not asserted by the
BQ76942 device, it remains in a high-impedance state and detects a voltage applied at the pin by a secondary
protector. The device can be configured to generate a PF if it detects a high signal at the FUSE pin.
The device can be configured to blow the fuse when a PF occurs. In this case, the device only attempts to blow
the fuse if the stack voltage is above a programmed threshold, based on a system configuration with the fuse
placed between the top of stack and the high-side protection FETs. If instead the fuse is placed between the
FETs and the PACK+ connector, then the device instead bases its decision on the PACK pin voltage (based
on configuration setting). This voltage threshold check is disregarded under certain cases, as described in the
BQ76942 Technical Reference Manual
.
Figure 12-1. FUSE Pin Operation
12.11 Cell Open Wire
The BQ76942 device supports detection of a broken connection between a cell in the pack and the cell
attachment to the PCB containing the BQ76942 device. Without this check, the voltage at the cell input pin of the
BQ76942 device may persist for some time on the board-level capacitor, leading to incorrect voltage readings.
The Cell Open Wire detection in the BQ76942 device operates by enabling a small current source from each
cell to VSS at programmable intervals. If a cell input pin is floating due to an open wire condition, this current
SLUSE14B – DECEMBER 2020 – REVISED DECEMBER 2021
48
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