circuitry and methods are provided for reducing rise time associated with signals on an open - drain or open - collector signal line . signal line voltage is monitored to determine if the signal line is being pulled low . if the signal line is not being pulled low , as indicated by signal line voltage exceeding a threshold level , additional pullup current is provided . the additional current may be provided gradually in relation to the signal line voltage , or may be provided in full whenever voltage exceeds the threshold . circuitry may also be provided to monitor voltage slew rate on the signal line , and to enable the additional pullup current only when the slew rate exceeds a positive threshold level .