I am trying to design a 12 volt smps supply from a -48 volt.
I went through the datasheets of top 224, but the input specification is 85-260 v ac, which means a minimum of 120 v dc.
Can I use this device for my design??
Where does this "-48V" come from? Is there a "paired" +48V? If there's no "accompanying" positive voltage, it doesn't matter that it's "-48V". Treat it as just (+)48V. Just take care with polarity (direction).
Then, use a buck converter circuit. How much current do you need? You can use one of many available switching regulators, such as L4971, L4972, L4973, L4975, L4976, L4977, L4970, etc.