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ADF4106 Output not varying

Question asked by crlanglois on Oct 15, 2012
Latest reply on Feb 10, 2016 by rbrennan

I am using an ADF4106 with a 15MHz REFin and am looking for a 1850MHz RF VCO output ~ 11.5V.

 

When I power up I'm getting 1696MHz out @ approx 2.2V.  I'm using the following SPI transactions in this order:

Initialization: 93

Function: 92

R Counter: 4

N Counter: 200F0D

 

After sending these the output drops to 1623MHz out @ approx 0.2V and the Digital Lock Detect goes high (locks).  I'm using latch values calculated with your Analog Devices Int-N PLL Software.  Am I sending the wrong bits somewhere?

 

I'm sending the latches in 3 byte words with some delay in between bytes (clock not running between) but I'm setting LE low before each set of 24 bits, and then high again after each latch.  I appear to be latching correctly because I'm able to set muxout to Digital Lock Detect.

 

Lastly, the REFin appears to have no effect on my output, with the reference there or removed the output is the same, varying the reference frequency also has no effect. (It is coming from an input connector and is being generated by an Agilent signal generator).

 

Any ideas would be greatly appreciated.

Thanks.

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