AD9559PCBZ datasheet(33/120 Pages) AD

33 / 120 page

Data Sheet

AD9559

Rev. 0 | Page 33 of 120

The AD9559 evaluation software includes a frequency planning

wizard that configures the profile parameters, based on the

input and output frequencies.

REFERENCE SWITCHOVER

An attractive feature of the AD9559 is its versatile reference

switchover capability. The flexibility of the reference switchover

functionality resides in a sophisticated prioritization algorithm

that is coupled with register-based controls. This scheme provides

the user with maximum control over the state machine that

handles reference switchover.

The main reference switchover control resides in the user mode

registers in the PLL_0/PLL_1 operational controls registers. The

reference switching mode bits (Bits[4:2] in Register 0x0A22 for

DPLL_0 and Register 0x0A42 for DPLL_1) allow the user to

select one of the five operating modes of the reference

switchover state machine, as follows:

•

Automatic revertive mode

•

Automatic nonrevertive mode

•

Manual with automatic fallback mode

•

Manual with automatic holdover mode

•

Full manual mode without holdover

In the automatic modes, a fully automatic priority-based algorithm

selects the active reference. When programmed for an automatic

mode, the device chooses the highest priority valid reference.

When two or more references have the same priority, REFA has

preference over REFB, and so on in alphabetical order. However,

the reference position is used only as a tiebreaker and does not

initiate a reference switch.

The following list gives an overview of the five operating modes:

•

Automatic revertive mode. The device selects the highest

priority valid reference and switches to a higher priority

reference if it becomes available, even if the reference in use

is still valid. In this mode, the user reference is ignored.

•

Automatic nonrevertive mode. The device stays with the

currently selected reference as long as it is valid, even if

a higher priority reference becomes available. The user

reference is ignored in this mode.

•

Manual with automatic fallback mode. The device uses the

user reference for as long as it is valid. If it becomes invalid,

the reference input with the highest priority is chosen in

accordance with the priority-based algorithm.

•

Manual with automatic holdover mode. The user reference

is the active reference until it becomes invalid. At that

point, the device automatically goes into holdover.

•

Full manual mode without holdover. The user reference is

the active reference, regardless of whether or not it is valid.

The user also has the option to force the device directly into

holdover or free run operation via the user holdover and user

free run bits. In free run mode, the free run frequency tuning

word register defines the free run output frequency. In holdover

mode, the output frequency depends on the holdover control

settings (see the Holdover section).

Phase Build-Out Reference Switching

The AD9559 supports phase build-out reference switching,

which is the term given to a reference switchover that

completely masks any phase difference between the previous

reference and the new reference. That is, there is virtually no

phase change detectable at the output when a phase build-out

switchover occurs.

AD9559PCBZ Datasheet(PDF) 33 Page - Analog Devices

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