Various protection circuits are built into Ricoh voltage regulators.
The Thermal Shutdown Circuit detects overheating of the voltage regulator if the output pin (VOUT) is shorted to the ground pin (GND) and stops the voltage regulator operation to protect it from damage.
For example, the Thermal Shutdown Circuit stops voltage regulator operation if the junction temperature of the R1150H Series becomes higher than 150°C. Additionally, if the junction temperature after the voltage regulator being stopped decreases to a level below 125°C, it restarts voltage regulator operation. (The temperature is different according to the product).
As a result the operation of the Thermal Shutdown Circuit causes the voltage 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).