If the controller is giving LO pulses and then there is no pulse from the controller side and the controller is retrying after 1 sec, this is due to either the OCP fault or OLP fault. For OCP fault detection, the voltage across the ISNS pin and PGND has to be probed. If the peak voltage at the ISNS pin touches the threshold of 3.5V, it is the OCP fault. To avoid OCP fault, R_isns must be reduced gradually, and TSET resistor divider must be adjusted accordingly by the design calculator to accommodate P_in vs VFBReplica graph within 2V-4V for no load to full load variation.

For OLP fault detection, FBReplica vs Pin graph has to be fitted one first prototype. The procedure to measure FBReplica in practical hardware is as follows:

1. Measure FBReplica voltage by inserting 5k resistor between feedback optocoupler emitter and ground as shown in Figure 1-2. The calculation can be done by Equation 1 .
   Figure 1-2 FBReplica Measurement Circuit
   Equation 1. $\begin{array}{c}FBReplica=\left(I_{FB}-\frac{V_{5k}}{5k}\right)\times R_{FBInternal}\#\left(1\right)\end{array}$
2. Plot FBReplica voltage vs Pin graph at different input power up to considering peak output power, not just up to full load output power, as shown in Figure 1-3.

If at any load, FBReplica touches 4.75V, then the fault at that load is OLP.