ZHCSH72I September 2011 – December 2017 LMK00301
The reference output (REFout) provides a LVCMOS copy of the selected input clock. The LVCMOS output high level is referenced to the Vcco voltage. REFout can be enabled or disabled using the enable input pin, REFout_EN, as shown in Table 5.
The REFout_EN input is internally synchronized with the selected input clock by the SYNC block. This synchronizing function prevents glitches and runt pulses from occurring on the REFout clock when enabled or disabled. REFout will be enabled within 3 cycles (tEN) of the input clock after REFout_EN is toggled high. REFout will be disabled within 3 cycles (tDIS) of the input clock after REFout_EN is toggled low.
When REFout is disabled, the use of a resistive loading can be used to set the output to a predetermined level. For example, if REFout is configured with a 1 kΩ load to ground, then the output will be pulled to low when disabled.