This state diagram shows how the active low going pulse generated by the momentary contact button has priority of the dimming state.  The BCM PWM signal can drive the IS32LT3175 to turn ON and OFF the LED light as shown state 1. In the next state 2, a button press causes a low going pulse to the LT3175 which turns ON the LED and the second pulse turns OFF LED at the fade speed set by the fade resistors. Notice the BCM PWM signal is ignored when the LED is enabled with the button press.  In state 3 the BCM PWM initially turns ON the LED and a pulse from the button turns OFF the LED independent of the BCM PWM signal.  States 4 and 5 show the momentary contact button will turn ON and OFF the LED independent of the BCM PWM.  Finally the last figure shows the fast response of the momentary contact button, the turn ON and OFF cycles can be terminated or initiated mid-cycle with every press of the button.