i saw some people did this
just wondering how can i do this in blender?
and any resource on it?
PNG can be saved as a 32bit file, but it only has 8 bits per channel.
HDRI is a 32 bit format and .EXR’s are at least 16 bit per channel, or 32bit.
So there will always be a loss of data. Will that be visible in a render? That is to be determined 
You can go old school, and split out the lighting info from the reflection detail. So a low res blurred HDRI for the color tone, and have a high res background (jpeg?) for the details.
This was quite common just a few years ago, and saved a lot of data on disk & RAM during rendering.
cheers,
rob