SLUUCF2C January 2021 – May 2022 BQ769142
When a Short Circuit in Discharge Latch or Overcurrent in Discharge Latch protection fault has occurred and the DSG FET is off, the device can be configured to recover when load removal is detected. This feature is useful if the system has a removable pack, such that the user can remove the pack from the system when a fault occurs, or if the effective system load that remains on the battery pack is higher than ≈20-kΩ when the DSG FET is disabled. The device will periodically enable a current source out the LD pin and will recover the fault if a voltage is detected at the LD pin above a 4 V level. If a low-impedance load is still present on the pack, the voltage the device measures on the LD pin will generally be below 4 V, preventing recovery based on Load Detect. If the pack has been removed from the system and the effective load is high, such that the current source generates a voltage on the LD pin above a 4 V level, then the device can recover from the fault. Note: typically a 10-kΩ resistor is connected between the PACK+ terminal and the LD pin, this resistance should be comprehended when considering the load impedance.
The Load Detect current is enabled for a time duration given by Protections:Load Detect:Active Time, then is disabled for a time duration given by Protections:Load Detect:Retry Delay, with this sequence repeating until the load has been detected as removed, or the accumulated time reaches Protections:Load Detect:Timeout. The timeout is included to prevent the device continuously attempting Load Detect indefinitely and causing long-term drain on the pack. If the timeout is met, the Load Detect function will no longer operate until the latched faults have recovered through another means, or the 0x009D LOAD_DETECT_RESTART() subcommand to restart the Load Detect is received.
If the Protections:Load Detect:Active Time is set to 0, then the Load Detect function is disabled. If the Protections:Load Detect:Retry Delay is set to 0, then the Load Detect current source will remain on continuously until timeout or recovery occurs.
The Load Detect current can be forced on or off through subcommands. If the Protections:Load Detect:Active Time is set to 0 and the 0x009E LOAD_DETECT_ON() subcommand is sent, the Load Detect current source will be enabled. If the 0x009F LOAD_DETECT_OFF() subcommand is sent, the Load Detect current source will be disabled.
When an SCDL or OCDL fault occurs and the DSG FET is disabled, the device may enter SLEEP mode, in which measurements of the LD pin voltage are only taken at intervals given by Power:Sleep:Voltage Time. It is recommended to set the Protections:Load Detect:Active Time longer than Power:Sleep:Voltage Time, to be sure that during each window when the current source is enabled, at least one measurement of the LD pin voltage will occur. The status of the Load Detect function is provided in 0x00 Control Status()[LD_TIMEOUT, LD_ON].