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. 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 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.

Thermal considerations such as input voltage, charge current, and system load should be taken into account when designing the charging system. It should not be designed such that the device not regularly reaches T_SHUT. Rather, device junction temperature should be limited to the Recommended Operating Temperature conditions.

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 THERM_REG setting. If the charge current is reduced to 0, the battery supplies the current needed to supply the SYS output.

To ensure that the 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

The θ_JA is largely driven by the board layout, board layers, copper thickness and the 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.