10 Power Supply RecommendationsThere is no restriction on the power-up sequence. In case the VDDOUT is applied first, TI recommends groundingVDD. In case the VDDOUT is powered while VDD is floating, there is a risk of high current flowing on the VDDOUT.The device has a power-up control that is connected to the 1.8-V supply. This will keep the whole devicedisabled until the 1.8-V supply reaches a sufficient voltage level. Then the device switches on all internalcomponents, including the outputs. If there is a 3.3-V VDDOUT available before the 1.8-V, the outputs staydisabled until the 1.8-V supply reaches a certain level.11 Layout11.1 Layout GuidelinesWhen the CDCE913 is used as a crystal buffer, any parasitics across the crystal affects the pulling range of theVCXO. Therefore, take care placing the crystal units on the board. Crystals must be placed as close to thedevice as possible, ensuring that the routing lines from the crystal terminals to XIN and XOUT have the samelength.If possible, cut out both ground plane and power plane under the area where the crystal and the routing to thedevice are placed. In this area, always avoid routing any other signal line, as it could be a source of noisecoupling.Additional discrete capacitors can be required to meet the load capacitance specification of certain crystal. Forexample, a 10.7-pF load capacitor is not fully programmable on the chip, because the internal capacitor canrange from 0 pF to 20 pF with steps of 1 pF. The 0.7-pF capacitor therefore can be discretely added on top of aninternal 10-pF capacitor.To minimize the inductive influence of the trace, TI recommends placing this small capacitor as close to thedevice as possible and symmetrically with respect to XIN and XOUT.Figure 24 shows a conceptual layout detailing recommended placement of power supply bypass capacitors. Forcomponent side mounting, use 0402 body size capacitors to facilitate signal routing. Keep the connectionsbetween the bypass capacitors and the power supply on the device as short as possible. Ground the other sideof the capacitor using a low-impedance connection to the ground plane.