7.3.1 Internal Current Limit

The TPS720 internal current limits help protect the regulator during fault conditions. During current limit, the output sources a fixed amount of current that is largely independent of output voltage. In such a case, the output voltage is not regulated, and is V_OUT = I_LIMIT × R_LOAD. The NMOS pass transistor dissipates (V_IN – V_OUT) × I_LIMIT until thermal shut down is triggered and the device is turned off. As the device cools down, it is turned on by the internal thermal shutdown circuit. If the fault condition continues, the device cycles between current limit and thermal shutdown. See the Thermal Considerations section for more details.

The NMOS pass element in the TPS720 has a built-in body diode that conducts current when the voltage at OUT exceeds the voltage at IN. This current is not limited, so if extended reverse voltage operation is anticipated, external limiting to 5% of rated output current is recommended.