ST9S313-DAG learn more.
This function is Supervisor IC.
Part Number : ST9S313-DAG
Package : DIP 8 Pin Type
Manufacturers : Sitronix
The IC is specially designed for switching power supply system. It provides over-voltage protection, over-current protection, under-voltage protection, on/off control and power good signal generating.
OVP/UVP (Over/Under-Voltage Protection) monitors 3.3V, 5V and double 12V to protect our power supply and PC, FPO goes to high when one of these supply voltages exceeds their normal operation voltage range.
Reference page : http://www.datasheetcafe.com/st9s429-pg14-datasheet-smps-supervisor/