  We present results on the determination of the observable ratio R=BR(H^+ ->
\tau \nu)/BR(H^+ -> t b-bar) of charged Higgs boson decay rates as a
discriminant quantity between Supersymmetric and non-Supersymmetric models.
Simulation of measurements of this quantity through the analysis of the charged
Higgs production process gb-> t b H^+ and relative backgrounds in the two above
decay channels has been performed in the context of ATLAS. A ~12-14% accuracy
on R can be achieved for \tan\beta=50, \mHc=300-500 GeV and after an integrated
luminosity of 300 fb^-1. With this precision measurement, the Large Hadron
Collider (LHC) can easily discriminate between models for the two above
scenarios, so long as \tan\beta > 20.
