Here you go, cheats! Since you can't beat that boss without dying, I have God mode for you (among others)
God mode- (Hold L1 and R1 the whole time) Press (on the D-pad) R, L, R, L, U, D, U, D
To find other cheats, hold the top shoulder buttons and fiddle around with patterns like that. I know of "Can't Be Struck" and "Damage x100". I'm not sure if there are any others. BY THE WAY, these are entered during gameplay, so you have to enter them each time you load a save.