ZHCSHN3D February 2018 – August 2019 TPS7A05
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 VOUT is 90% of VOUT(nom) the current limit is ICL(typical); however, if VOUT is forced to 0 V the current limit is ISC (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 VOUT > 500 mV (typ), thus limiting current to ICL(typical) and, when VOUT is approximately 0 V, current is limited to ISC (typical) to ensure normal start-up into a variety of loads.
The foldback current limit is disengaged when IOUT < 1 mA (typical) to reduce IQ. As such, the current-limit loop takes longer to respond to a current-limit event when IOUT < 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.