http://e2e.ti.com/support/clocks/b/clocksblog/archive/2012/04/26/cdcm1802-cdcm1804-enabling-if-input-clock-is-applied.aspxIn the datasheet TI describes that the device needs 1us to settle internal voltages and bandgap after EN goes high: However, if the input clock is already available, there is no issue to enable the outputs of CDCM1802/CDCM1804. The device stillen-US6.x Production