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AD9552 only locking with ref doubler enabled, why ?

Question asked by AndyW on Jun 10, 2012
Latest reply on Jun 10, 2012 by AndyW

I've just received an AD9552 eval board (Rev D), chip date code 1134.

 

While putting it through it's paces with the ADI software (V1.0), the PLL only seems to lock with the reference doubler enabled.

The software reports a locked PLL, even when the LOCKED LED on the board is off - external freq counter shows that the PLL is indeed NOT locked.

Enabling the reference doubler and the PLL instantly snaps to freq and the on-board LED lights up.

 

This behaviour occurs regardless of whether I select the on-board xtal or use an external reference, and across the full range of output frequencies.

 

I've looked for errata and similar discussions here and found nothing.

 

Any ideas what's going on ?

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