ADF5901 programming issue


I have designed a custom board with adf5901. After power up of the board, I enable the chip by supplying 2.5V to CE pin. Then I try to write register R3 to program the MUXOUT to give 3.3V (high). But looks like the chip is not responding at all. The MUXOUT is stuck at 0.6V and there is no difference in any of the pin voltages. I cross checked the SPI timing using scope and it all looks fine to me. I got the chip replaced thinking it was damaged, but then nothing was fixed and I still see the same. I bought the radar mmic2 eval board to cross check the pin voltages one on one. I didnt see any major problem. Also compared the SPI transaction on scope to see no difference between eval board and my board. Is there something that I am missing? I want to know if the sequence of register write is correct.

1. I power up the board and set chip_enable = 1.

2. Then I write the register R3 with 'h01891803 only once. (No double buffering)

Is this sufficient to set the MUXOUT pin to 3.3V?

Also, can I find the log of eval board GUI somewhere? Maybe I can trace the SPI writes performed by click of each button in the GUI so that I can replicate that in my software. That will be very helpful.



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  • 0
    •  Analog Employees 
    on Apr 13, 2021 11:26 PM in reply to gensysco

    Your schematic looks OK. I don't see anything that would prevent you from writing to the ADF5901.

    When you enable the chip by bringing CE high, what voltage do you measure on VREG (pin 18)? Output should be ~1.9V.
    Is CE brought low at any point? This will power down the part and clear the register settings.

    What SPI clock frequency are you using? Max frequency is 20 MHz.
    The timing specs in table 2 on page 4 of the datasheet must be respected when communicating with the part.

    Logic input voltages must be within the range 0V to 0.6V (logic low) and 1.4V to DVDD (logic high).

    Do you have a scope plot of your register writes?

  • Hi  

    We figured out the issue. We were getting 2.1V on VREG pin. When we had a closer look at the board and schematic, we saw that the VREG was connected to 220pF cap instead of 220nF cap. We replaced the cap and the got VREG to be 1.87V. After making this change, the SPI transactions are working correctly.

    Thanks for your help.

    Best regards

  • 0
    •  Analog Employees 
    on Apr 16, 2021 9:14 AM in reply to gensysco

    Thanks for the update - glad you were able to resolve the issue.