I have a project in which input voltage will vary from 1.5V to 0.9V (Alkaline battery) and output voltage is fixed to 3.3V with maximum load current 50mA.I want operation to shutdown after 0.9V as battery cutoff voltage is 0.9V. I'm looking for a boost IC controller with integrated switch and synchronous rectification and other features in it. Please suggest me some useful boost IC parts.