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Problems with AD9956´s IO_Update Signal

Question asked by rodney on Jan 5, 2012
Latest reply on Jan 7, 2012 by rodney



I´m  designing a circuit based on ADI´s AD9956 like the typical aplication  circuit showed on Figure 24. LO and Baseband Modulation Generation"  AD9956 datasheet, page 16.



On page 12 says:


PIN   Mnemonic         Description

20      I/O_UPDATE     This input pin, when set high, transfers the data from  the I/O buffers  to the internal registers on the rising edge of the  internal                                  SYNC_CLK,  which can be  observed on SYNC_OUT.


On  that typical application the SYNC_CLK signal is the output of R  divider, and the PLLref signal is provided by a crystal. But, i need  that AD9956 recognice the I/O_Update signal to:

- Enable cristal oscillator

- Configure CML driver

- Configure R diveder

-Configure N and M dividers.

- Others configuratons.


How is it possible if I dont have the SYNC_CLK signal when I start AD9956?


For example, on AD9912 from ADI too the I/O_Update signal is completely asynchronous.


Can some one clear my doubt?