ADF4355-3 Thermal Issue

Hi,

I have been having repeatable issue with the ADF4355-3 where heating up the IC will cause unstable RF output. What I'm seeing is the Lock Detect mux output is toggling between '1' and '0' repeatedly. When I update the registers with a new frequency the output will be stable and no other issue seems to reoccur. I know that the VCO output is dependent on temperature and writing to register 10 will update its temperature. Here's a picture of when the issue occurs https://imgur.com/a/Y9hpF8n. The frequency I was generating is 370MHz. 

My question is what's the best way to not have the unstable RF output occur once the IC's registers are set? My application requires the IC to not have any instability due to temperature transitions. 

Thank your for your time any advice is greatly appreciated!

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  • I won't be able to provide the schematic unfortunately. The differential input comes from the HMC832A and the loop filter is the recommended 35kHz filter from the datasheet. 

    Register settings:

    R12: 0x0001050C

    R11: 0x0081200B

    R10: 0x00C026BA

    R9:   0x34067F99

    R8:   0x1A69A6B8

    R7:   0x100002E7

    R6:  0x356489B6

    R5:  0x00800025

    R4:  0x32008B84

    R3:  0x00000003

    R2:  0x00080032

    R1:  0x05AAAAA1

    R0:  0x00200600

    Note: This is used to generate a 740MHz output, but we have another IC for RF divider by a factor of 2 so it should be 370MHz result.

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