CDCE62002 datasheet(30/49 Pages) TI

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Auxiliary Input Port

External Feedback Mode

PFD/

Feedback

Divider

Divby 1

REF_IN

CDCE62002

SCAS882A – JUNE 2009 – REVISED JULY 2009.............................................................................................................................................................. www.ti.com

The auxiliary input on the CDCE62002 is designed to connect to an AT-Cut Crystal with a total load capacitance

of 8 pF to 18pF. One side of the crystal connects to Ground while the other side connects to the Auxiliary input of

the device. The circuit accepts crystals from 2 to 42 MHz.

Since the Auxiliary input operates between 0 and 2 Volts with a crystal, it can accept single-ended signals (e.g.,

LVCMOS). Electrically, it is equivalent to an LVCMOS input buffer with 8 pF of input capacitance.

Figure 24. CDCE62002 Auxiliary Input Port

The auxiliary input on the CDCE62002 is to serve as an external feedback port if Bit (10) in Register 0 is set to

“1” and input smart Mux setting is set to Reference input. In addition, The Reference Divider and the input divider

have to be set to divide by 1. This feature is implemented to allow direct access to the PFD of the PLL. The

delay from Reference input to PFD and from Auxiliary Reference to PFD is not matched. However, in close loop

system where the device output is fed to close the loop the delay difference between the Reference and External

feedback path will cancel out.

Figure 25. CDCE62002 in External Feedback Mode

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