Short for Moisture Sensitivity Level, MSL is a JEDEC (Joint Electron Device Engineering Council) standard established for the purpose of preventing device failure due to volumetric expansion of atmospheric moisture introduced into the resin package of semiconductor devices during reflow. The floor life of IC packages, during which the components must be mounted and reflowed after opening the moisture-resistant packaging, is broken down into 8 MSL levels.
The BD8152FVM integrates a FET, making external FET drive, and therefore step-up 55V/3A output, impossible. However, inputting IC drive voltage (i.e. 12V) to the Vcc of the BD9306AFVM controller allows for high input/output voltage operation.
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.