8.3.3.6 Charging Safety Timer

The bq24193 has safety timer to prevent extended charging cycle due to abnormal battery conditions.

In default mode, the device keeps charging the battery with 5-hour fast charging safety timer regardless of REG05[2:1] default value. At the end of the 5 hours, the EN_HIZ (REG00[7]) is set to signal the buck converter stops and the system load is supplied by the battery. The EN_HIZ bit can be cleared to restart the buck converter.

In host mode, the device keeps charging the battery until the fast charging safety timer expired. The duration of safety timer can be set by the REG05[2:1] bits (default = 8 hours). At the end of safety timer, the EN_HIZ (REG00[7]) is cleared to signal the buck converter continues to operation to supply system load.

The safety timer is 1 hour when the battery is below BATLOWV threshold. The user can program fast charge safety timer through I²C (REG05[2:1]). When safety timer expires, the fault register REG09[5:4] goes 11 and an INT is asserted to the host. The safety timer feature can be disabled via I2C (REG05[3]).

The following actions restart the safety timer:

• At the beginning of a new charging cycle
• Toggle the CE pin HIGH to LOW to HIGH (charge enable)
• Write REG01[5:4] from 00 to 01 (charge enable)
• Write REG05[3] from 0 to 1 (safety timer enable)
• Write REG01[7] to 1 (software reset)

During input voltage/current regulation or thermal regulation, the safety timer counts at half clock rate since the actual charge current is likely to be below the register setting. For example, if the charger is in input current regulation (IINDPM) throughout the whole charging cycle, and the safety time is set to 5 hours, the safety timer will expire in 10 hours. This feature can be disabled by writing 0 to REG07[6].