A circuit, delay-locked loop, memory device, system and method of synchronizing a clock are described. A circuit generally includes a delay line configured to delay an external clock signal to produce a substantially in-phase output clock signal, a main loop configured to control delay through the delay line, and a secondary loop configured to adjust delay through the main loop. The clock synchronization method generally includes adjusting a delay along a delay line in response to a first phase difference between an input clock to the delay line and a shared clock signal delayed by a shared dynamic I/O model of an output driver. The method further includes adjusting the shared dynamic I/O model in response to a second phase difference between an output clock signal and the shared clock signal.