how to avoid transparent background converting to white in smart object(psb )when image trace High Fidelity as we have the option of ignore white upto 16 colors trace.

i have a psd image file in photoshop cc 2014 that has transparent background layer. I wanted it to convert to vector. The best option i saw was to first convert it to smart object in photoshop via Layer->Smart Objects-> Convert to smart Object. then exported it to a psb. Then i opened the file in illustrator and applied the image trace tool but the transparent background got converted to white but i had the option of ignore white upto 16 colors trace. But in case of High Fidelity Conversion, the ignore white option is not available, what should I do now?