How does the line under-voltage protection circuitry of the LM5020 work?
The LM5020 contains a line Under-Voltage Lockout (UVLO) comparator and precision 1.25V voltage reference. An external resistor divider connected from the line input to ground programs the UV threshold and hysteresis. The UVLO comparator holds the controller in an off state until the UVLO pin exceeds 1.25V. When the UVLO threshold is achieved, a 20 µA hysteresis current source is activated to flow out of the UVLO pin through the external resistor network. This current source raises the voltage at the UVLO pin to avoid false triggering due to noise. The UVLO pin can also be used to implement a remote enable/disable function. The converter is disabled by simply pulling UVLO below the 1.25V comparator threshold using an external switch or transistor.
