At light load condition when the controller is working at Discontinuous Current Mode (DCM), it is better to turn on the switching MOSFET when drain voltage is at its minimum voltage level to achieve a maximum efficiency. An external resistor connected from DRV to GND adjusts the delay between the drain waveform falling below V_IN and the DRV rising edge, allowing the turn on transition to be aligned to the valley minimum accurately over a wide range of idle ring oscillating frequency. Different resistor values of R_DG set eight different delay times(T_ZCDR0 – T_ZCDR7).

Fine-tune the R_DG value for a given switching MOSFET and PFC inductor. Figure 2-2 and Figure 2-3 list the resistor values and the delay times as shown in the data sheet.

Figure 2-2 Eight Different R_DG Resistors Settings

Figure 2-3 Eight Different T_ZCDR Delay Times