The TPS2556-Q1 and TPS2557-Q1 devices self-protect by using two independent thermal sensing circuits that monitor the operating temperature of the power switch and disable operation if the temperature exceeds recommended operating conditions. The TPS2556-Q1 and TPS2557-Q1 devices operate in constant-current mode during an overcurrent condition, which increases the voltage drop across power switch. The power dissipation in the package is proportional to the voltage drop across the power switch, which increases the junction temperature during an overcurrent condition. The first thermal sensor (OTSD) turns off the power switch when the die temperature exceeds 135°C (min) and the part is in current limit. Hysteresis is built into the thermal sensor, and the switch turns on after the device has cooled approximately 20°C.

The TPS2556-Q1 and TPS2557-Q1 devices also have a second thermal sensor (OTSD2). This thermal sensor turns off the power switch when the die temperature exceeds 155°C (minimum) regardless of whether the power switch is in current limit, and turns on the power switch after the device has cooled approximately 20°C. The TPS2556-Q1 and TPS2557-Q1 devices continue to cycle off and on until the fault is removed.