Note that at full load and at the lowest input voltage the magnitude of RN is the smallest (we will use this fact later). For example, a 3.3VOUT, 30A half-brick converter that is 90% efficient (because it uses synchronous rectifiers) will draw an input current of about 3A when its input voltage is 36V. Under this condition RN = -12Ω. At the nominal input voltage of 48V, the full-load input current is only 2.3A and RN = -21Ω