This paper investigates the effect of the integrator gain on subharmonic oscillation boundary in switching converters with fixed frequency pulse width modulation (PWM) with an integrative feedback loop. First, the exact state-space switched model of the converter is revisited and then a closed-form expression for predicting this phenomenon is presented. The use of this expression is illustrated by means of two different examples f switching converters. While in voltage mode control, the integral action can be ignored for predicting subharmonic oscillation, it is shown the integral action in the current loop has a significant effect on this phenomenon.