A magnetic field sensor apparatus includes a sensor signal generator generating a sensor signal responsive to a magnetic field. A switching level provider provides during a power up mode a switching level based on a most recently updated valid one of a first and a second value of a default switching level. If an update triggering condition occurs, the not most recently updated one of the first and second values of the default switching level is updated and the most recently updated one of the first and second values of the default switching level is maintained unchanged until a next update triggering condition occurs, so that the first and second values of the default switching level are updated alternately on consecutive triggering conditions.