CDCE62005 datasheet(63/76 Pages) TI

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Lock Detect

PFD/

FromInputDivider

FromFeedback Divider

ToLoopFilter

FromInputDivider

FromFeedback Divider

Locked

Unlocked

FromInputDivider

FromFeedback Divider

25 24 23 22

Lock Detect Window (Max)

Lock Detect Window Adjust

(a)

(b)

27 26

FromDigital

Lock Detector

PLL_LOCK

1 = Locked

O = Unlocked

(c)

CDCE62005

www.ti.com........................................................................................................................................................................................... SCAS862 – NOVEMBER 2008

Digital Lock Detect

The CDCE62005 provides both an analog and a digital lock detect circuit. With respect to lock detect, two signals

whose phase difference is less than a prescribed amount are ‘locked’ otherwise they are ‘unlocked’. The phase

frequency detector / charge pump compares the clock provided by the input divider and the feedback divider;

using the input divider as the phase reference. The digital lock detect circuit implements a programmable lock

detect window. Table 43 shows an overview of how to configure the digital lock detect feature. When selecting

the digital PLL lock option, the PLL_LOCK pin will possibly jitter several times between lock and out of lock until

the PLL achieves a stable lock. If desired, choosing a wide loop bandwidth and a high number of successive

clock cycles virtually eliminates this characteristic. PLL_LOCK will return to out of lock, if just one cycle is outside

the lock detect window or if a cycle slip occurs.

Figure 36. CDCE62005 Digital Lock Detect

Table 43. CDCE62005 Digital Lock Detect Control

DIGITAL LOCK DETECT

Bit Name

→

ADLOCK

LOCKDET

LOCKW(3)

LOCKW(2)

LOCKW(1)

LOCKW(0)

→

5.27

5.26

5.25

5.24

5.23

5.22

Lock Detect Window

Analog Lock

1 cycle in lock window triggers a lock

64 continuous cycles in lock window triggers a

lock

Narrow Window

One step wider than narrow window

Two steps wider than narrow window

Three steps wider than narrow window

Four steps wider than narrow window

•

Widest Window

Reserved

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