Gui_download Write_field_separator ##BEST##

I am using the fucntion gui_download with the option WRITE_FIELD_SEPARATOR = 'X' ., i am trying to get the same file with the open dataset, i have tried with open dataset in text mode and concatenating the fields with cL_ABAP_CHAR_UTILITIES=>HORIZONTAL_TAB befor transfer, but it isnt identical.

Gui_download Write_field_separator