The NB3N853501E is a low skew 3.3 V supply 2:1:4 clock distribution fanout buffer. An Input MUX selects one of two LVCMOS/LVTTL CLK lines by the CLK_SEL pin (HIGH for CLK1, LOW for CLK0) using LVCMOS/LVTTL levels. A CLK_EN pin can enable or disable the outputs synchronously to eliminate runt pulses using LVCMOS/LVTTL levels (HIGH to enable outputs, LOW to disable output).