ZHCSBB1D July 2013 – March 2018 UCC28740
The PCB tracks from the opto-coupler to the FB pin should have minimal loop area. If possible, it is recommended to provide screening for the FB trace with ground planes. A resistor to GND from the FB pin is recommended to speed up the turnoff time of the opto-coupler during a heavy load step transient. This resistor should be placed as close as possible to FB and GND with short traces, the value of this resistor, RFB4, is detailed in the Application and Implementation section.