LDO Regulator Application Note
Various protection circuits are built into Ricoh regulators.
The Thermal Shutdown Circuit
The Thermal Shutdown Circuit shown in the blue ellipse, detects overheating of the regulator if the output pin (VOUT) is shorted to the ground pin (GND) etc. and stops regulator operation to protect it from damage.
For example, the Thermal Shutdown Circuit stops regulator operation if the junction temperature of the R1150H Series becomes higher than 150°C. Additionally, if the junction temperature after the regulator being stopped decreases to a level below 125°C, it restarts regulator operation. (The temperature is different according to the product.)
As a result the operation of the Thermal Shutdown Circuit causes the regulator repeatedly to turn OFF and ON till the causes of overheating are removed. As a consequence a pulse shaped output voltage occurs. Please prevent this situation.
In the datasheet it is shown as a thermal shutdown detection temperature (TTSD) and a thermal shutdown release temperature (TTSR).