At the time of passing of resolution for the issue of convertible debeture, authorised capital is not a matter of concern.
However when you are in process to convert the convertible debeture in to equity shares you have to take care of authorised capital.
So when you convert the convertible debeture then remember proposed share capital should not be more than authorised capital. So the deciding time is conversion of convertible debeture and not the issue of convertible debeture.