7.3.6 Internal Foldback Current Limit

The internal foldback current limit circuit is used to protect the LDO against high-load current faults or shorting events. The foldback mechanism lowers the current limit as the output voltage decreases, and limits power dissipation during short-circuit events while still allowing for the device to operate at the rated output current; see Figure 15.

For example, when V_OUT is 90% of V_OUT(nom), the current limit is I_CL (typical); however, if V_OUT is forced to 0 V, the current limit is I_SC (typical).

In many LDOs, the foldback current limit can prevent start up into a constant-current load or a negatively-biased output. A brick-wall current limit is when there is an abrupt current stop after the current limit is reached. The foldback mechanism for this device goes into a brick-wall current limit when V_OUT > 500 mV (typical), thus limiting current to I_CL (typical). When V_OUT is approximately 0 V, current is limited to I_SC (typical) in order to provide normal start up into a variety of loads.

Thermal shutdown can activate during a current-limit event because of the high power dissipation typically found in these conditions. To provide proper operation of the current limit, minimize the inductances to the input and load. Continuous operation in current limit is not recommended.