wala namang batas na nagsasabing mandatory and separation pay, depende yan sa kumpanya, and sometimes CBA kung may union. hanggang 13mos lang ang coverage ng labor code.
and you resigned, that means hindi ka entitled. separation pay usually applies sa mga natanggal for valid reason (like loss of business, lugi kumpanya, etc)
to give you example, innodata closed shops in 2002, all 3000+ regular employees were giver separation pay, calculatio nwas based on the CBA ng union at innodata.
PAL is another story, tinanggal mga empleyado kasi nagwelga habang bumabagyo, daming international passenger ang na stranded, nasira pangalan ng pinas. so terminated lahat ng empleyado, and they're battling it out on court. last offer ng PAL aside from 1mos/yr is libreng sakay sa eroplano all the time including familiy members, anywhere in the world.