The device has an internal current-limit circuit that protects the regulator during transient high-load current faults or shorting events. In a high-load current fault, the current limit scheme limits the output current to the current limit (I_CL). I_CL is listed in the Electrical Characteristics table.

The output voltage is not regulated when the device is in current limit. When a current-limit event occurs, the device begins to heat up because of the increase in power dissipation. When the device is in current limit, the pass transistor dissipates power [(V_I – V_O) × I_CL]. For more information on current limits, see the Know Your Limits application note.

To achieve a safe operation across a wide range of Input voltage, the UA78M also has a built-in protection mechanism with current limit. The protection mechanism decreases the current limit as input-to-output voltage increases and keeps the power transistor inside a safe operating region for all values of input-to-output voltage. This protection is designed to provide some output current at all values of input-to-output voltage limits defined in the Recommended Operating Conditions table. Figure 6-1 shows the behavior of the current limit variation.

Figure 6-1 Current-Limit vs V_Head-room Behavior (New Chip)