Once NS, target VOUT, output rectifier drop VRECT, and the secondary-side-to-bias leakage inductance LLK(sec_bias) are known, the required value for RB can be calculated. Referring to Equation 10, LLK(sec_bias) can be approximated as a percentage of the secondary-side-referred magnetizing inductance LSEC. (See Magnetic Sense Resistor Network Selection for details).
In this case, RB may need to be empirically adjusted to achieve the required exact output set-point, especially if VRECT varies or is not known precisely. For this reason, it is recommended that RB should be implemented on the system PCB as two parallel resistors RB1 and RB2 as shown in Figure 28, to allow easier fine-tuning of set-point. For set-point tuning, only RB should be adjusted. RA should never be adjusted, because to do so would affect the line sense gain and introduce errors into the line voltage measurement.