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 its rated output current; see Figure 29.

A foldback example for this device is that 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. The foldback mechanism for this device goes into a brick-wall current limit when V_OUT > 500 mV (typ), thus limiting current to I_CL(typical) and, when V_OUT is approximately 0 V, current is limited to I_SC (typical) to ensure normal start-up into a variety of loads.

The foldback current limit is disengaged when I_OUT < 1 mA (typical) to reduce I_Q. As such, the current-limit loop takes longer to respond to a current-limit event when I_OUT < 1 mA (typ).

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