During operation, to protect the device from damage due to overheating, the junction temperature of the die, T_J, is monitored. When T_J reaches T_{SHUT_RISING}, the device stops charging operation and VSYS is shutdown. If in the case where T_J > T_{SHUT_RISING} prior to power being applied to the device (either battery or adapter), the input FET or BATFET will not turn ON, regardless of the TSMR pin. Thereafter if temperature falls below T_{SHUT_FALLING}, the device will automatically power up if VIN is present or if in battery only mode.

During the charging process, to prevent overheating in the device, the device monitors the junction temperature of the die and reduces the charging current once T_J reaches the thermal regulation threshold (T_REG) based on bits set by the THERM_REG setting. If the charge current is reduced to 0, the battery supplies the current needed to supply the SYS output. Thermal regulation can be disabled through I²C.

Ensure that system power dissipation is under the limit of the device. The power dissipated by the device can be calculated using the following equation:

P_DISS = P_SYS + P_BAT

Where:

P_SYS = (V_IN – V_SYS) * I_IN

P_BAT = (V_SYS – V_BAT) * I_BAT

The die junction temperature, T_J, can be estimated based on the expected board performance using the following equation:

T_J = T_A + θ_JA * P_DISS

θ_JA is largely driven by board layout. For more information about traditional and new thermal metrics, see the IC Package Thermal Metrics Application Report. Under typical conditions, the time spent in this state is very short.