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ADF4360-7 Locking Problem and External Inductor Issue


Hi,

I have questions regarding PLL locking and external inductors.

I am trying to get a constant RF output from the device. 
I use ADF4360-x Evaluation Software to obtain register values and send them via a microcontroller.
I use ADIsimPLL to obtain the schematic.


In my case, I want to have 500 MHz output signal. 
I followed the schematics that Eval. Board and ADIsimPLL suggest.
The ADIsimPLL schematic and ADF4360 Eval. software output and my schematic' pictures are attached.

The other issue is external inductors. ADIsimPLL suggests me to use 3.15nH however, ADF4360-7 datasheet says that I should use around 12nH to get 500 MHz at the output. (page 22, Figure 24. Output Center Frequency vs. External Inductor Value)

Please note that for the loop filter I couldn't find the exact values that ADIsimPLL suggests on the market.
Instead of 282pF, I use 270pF
     "       "   13.6K, "  "      13.3K
     "       "   58.3pF, " "      56pF

I could not get ADF4360-7 locked.

What am I missing ?



Thanks in advance.



Image alignment
[edited by: FrequencyModulator at 1:46 AM (GMT 0) on 24 Apr 2020]
  • Hi,

    There is "Configuration Option" selection tab as given below. You can click that button and select 500 MHz which returns 15.3 nH external inductance value.

    For the loop filter element values, you can use "PLL Options" under Edit. You can set the standard for values to be used. Also, you can change Loop filter control from Phase Margin to Component and enter your values manually as given below.

    Regards,

    Kudret


  • Hi Kudret,

    I've just tried to obtain 420MHz output signal. ADIsimPLL says I should use 22nH. I removed 3.15nH inductors from the board and inserted 22nH. Again, using ADF4360 Eval. software I obtained register values send them through SPI.
    I configured muxout to be Digital output and muxout pin is connected to a led on my board. 

    But, the device is still not locked.

    I've also checked I get 10MHz sinusodial output from the oscillator.



    Here are the register values I used this time.


  • Hi,

    It is recommended to set prescaler to 8/9 when VCO frequency is below 700 MHz (See A and B counter section of datasheet).

    You need to be careful about the programming sequence such that R Counter Latch, Control Latch and N Counter Latch, respectively. Also, there is timing specifications between writing registers. See Power-Up section of datasheet.

  • Hi,

    I've set prescaler to 8/9.

    Here is how I program the IC

    Pull LE pin low
    Send R counter latch bits.
    Wait for 25ms
    Send Control Latch bits.
    Wait for 25ms
    Send N counter Latch bits
    Wait for 25ms.
    Pull LE pin high.

    But, still couldn't have the PLL locked.