ZHCSTD3B June 2022 – October 2023 BQ756506-Q1
PRODUCTION DATA
The UART interface requires the TX and RX pins are pulled up through a 10-kΩ to 100-kΩ resistor. Do not leave TX and RX unconnected. The TX must be pulled high to prevent triggering an invalid communications frame during the idle state. When using a serial cable to connect to the host controller, connect the TX pull-up on the host side and the RX pull-up to the CVDD on the device side.
NFAULT pin for device, if not used, must be left floating. Otherwise, pull it up with 100-kΩ to CVDD.
Important note for NFAULT with <6S applications:
The number of active channels cannot be reduced below six. This means that unmasked faults on unused channels can cause NFAULT to assert. Follow the subsequent directions in order to prevent unused channels from causing unnecessary NFAULT assertions.
Disable the undervoltage checks on unused channels via the UV_DISABLE register. If this isn’t used, the channels will always flag UV faults when the OVUV protector is enabled.
To disable the cell balancing diagnostic, set the balancing timer (registers CB_CELLn_CTRL) to 0s on unused channels. This will prevent the diagnostic from running on these channels.
There is no way to prevent open wire diagnostics from triggering faults on unused channels. If a system uses NFAULT, the open wire faults must be masked before running the diagnostics and the results must be read manually. Then the faults must be cleared and the masks disabled. Follow this procedure to run open wire checks:
Mask comparison faults via the MSK_COMP register
Turn on the VC pins (or CB pins) current sink or source through DIAG_COMP_CTRL3[OW_SNK1:0]
Wait for the expected dV/dt time of the external capacitor to deplete to the detection threshold if there is an open wire fault.
For VC open wire detection, select DIAP_COMP_CTRL3[COMP_ADC_SEL2:0] = OW CB check (that is, 0b011).
The device compares all active VCELL measurements (for VC open wire) or AUX CELL measurements (for CB open wire) against the [OW_THR3:0] threshold setting.
When the comparison is completed, ADC_STAT2[DRDY_VCOW] = 1 for VC open wire (or [DRDY_CBOW] = 1 for CB open wire). Host then turns off all current sinks and sources through DIAG_COMP_CTRL3[OW_SNK1:0]
Manually read the open wire fault registers (FAULT_COMP_VCOWx or FAULT_COMP_CBOWx)
The MCU should take action if used VC/CB channels indicate faults; ignore faults on unused VC/CB channels.
Clear faults
Unmask comparison faults via MSK_COMP