The BD9006 features a minimum ON time of 250ns. For example, with a switching frequency of 100kHz the minimum ON duty ratio is 250ns/(1/100kHz) x 100 = 2.5%. So with an input voltage of 35V the minimum output voltage is 35V x 2.5% = 0.875V. It is possible to achieve the desired output by decreaseing the switching frequency. However, the inductor and capacitor values will increase.