This pin has dual functions: enable input and line undervoltage sense.During normal operation, switching of the power MOSFET is controlledby this pin. MOSFET switching is terminated when a current greaterthan a threshold current is drawn from this pin. Switching resumeswhen the current being pulled from the pin drops to less than athreshold current. A modulation of the threshold current reducesgroup pulsing. The threshold current is between 75 μA and 115 μA.The ENABLE/UNDERVOLTAGE pin also senses line undervoltageconditions through an external resistor connected to the DC linevoltage. If there is no external resistor connected to this pin,TinySwitch-4 detects its absence and disables the line undervoltagefunction