No.

Name

Function

6

COMP

Output pin of the trans-conductance Error Amplifier (OTA). A compensation network is placed between

this pin and GND to allow stability of the control loop and ensure high PF and THD. To avoid

uncontrolled rise of the output voltage at light or zero load, when VCOMP < VCOMP_S (1 V typ. Burst

Mode condition) the gate driver pin (GD) is forced low and the switching activity is stopped. If the Burst

Mode condition is triggered when GD is high, the system is allowed to complete the current on-time and

the system stoppage takes place after GD falling edge.

The pin can be also used to disable the device by forcing VCOMP < VCOMP_DIS (0.7 V typ.) by means of

an external pull-down active network.

7

N.C.

High voltage spacer. This pin is not internally connected to isolate the high voltage section and ease

compliance with safety regulations (creepage distance) on the PCB.

8

HV

High voltage start-up generator input / AC voltage sensing input. The pin, able to withstand 800 V, has

to be connected to the AC side of the input bridge via a pair of diodes (1N400x type) to sense the AC

input voltage. If the voltage on the pin is higher than VHV_START (29 V typ.), an internal pull-up circuit

charges the capacitor connected between the pin VCC and GND. Initially the current is low for safety

in case of a shorted VCC, and then it goes to the normal level as far as the VCC pin reaches the

start-up threshold (VCC_ON). The generator is re-enabled when the voltage on the VCC pin falls below

the UVLO threshold (VCC_OFF).

The pin is used also to sense the AC voltage, which is used by the AC brownout, the input voltage

feedforward and the THD-CCM optimizer functions.

An internal logic circuit detects that the unit has been detached from the power line; if this event occurs

then, the HV pin sinks a current to discharge the X-capacitors of the EMI filter to a safe level. This

allows the unit to meet safety regulations (such as IEC 61010-1 or IEC 62368-1) without using the

traditional discharge resistor in parallel to the X-capacitor, thus saving the associated power losses and

enabling ultra-low consumption in standby conditions. In case an AC brownout condition is detected

the internal generator is alternatively turned on and off and, as a consequence, the voltage at VCC pin

cycles between the start-up threshold and the UVLO threshold.

L4985

Pin connection and functions

DS13769 - Rev 3

page 5/27