External Crystal on AD4115 and EVAL-AD4115SDZ

I just purchased an EVAL-AD4115SDZ so I could evaluate the AD4115. I've noticed that it works as expected after a reset using the internal clock - writing 0x0000 to the ADCMODE register and dropping CS indicates continuous conversions at 125Khz on the RD/MISO pin. But as soon as I write 0x00C0 to the ADCMODE register (enable external clock), the continuous data stream stops. When I look at the CLK test point with my oscilloscope, I am not seeing any oscillation. So my question is: did I receive a defective eval board or is there an undocumented issue with the AD4115. For the record, I also have the AD4112 eval board and the external XTAL oscillator works correctly. 



Fixed typo
[edited by: WallyBalls at 1:58 PM (GMT -5) on 15 Jan 2021]
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  • 0
    •  Analog Employees 
    on Jan 18, 2021 5:42 AM 2 months ago

    Hi, 

    Any potential crystal start-up issue might be unique to the customer’s Eval boards, e.g. poor solder connection to the crystal, caps value installed, layout, etc.. Though one thing I noticed between AD4114/15 EVB and AD4111/12 EVB are the caps in the AD4114/15 boards are installed which supposedly be DNI. I'll be at the office mid or later this week and try to get and setup both boards.

    Because of this possible crystal failed to start issue because of the nature of the crystal circuitry, I was also thinking now that this could also be the cause of the original problem on your other issue regarding the AD4112 in continuous read mode. If the crystal oscillator failed to start after switching to external crystal and continuous read mode, then that could explain why /RDY initially pulses correctly after the reset, but fails to pulse after the write to MODE & IFMODE. The external crystal circuitry especially during start up is really sensitive on  any disturbances e.g. when supplying an SCLKs. Some of your later examples do not switch to a crystal and there should be no dependence on the Mux-selection regardless of clock-source. So might worth performing the same test while keeping the internal oscillator active instead. 

    I'll confirm this on my side and come back to you on this. 

    Thanks,

    Jellenie

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  • 0
    •  Analog Employees 
    on Jan 18, 2021 5:42 AM 2 months ago

    Hi, 

    Any potential crystal start-up issue might be unique to the customer’s Eval boards, e.g. poor solder connection to the crystal, caps value installed, layout, etc.. Though one thing I noticed between AD4114/15 EVB and AD4111/12 EVB are the caps in the AD4114/15 boards are installed which supposedly be DNI. I'll be at the office mid or later this week and try to get and setup both boards.

    Because of this possible crystal failed to start issue because of the nature of the crystal circuitry, I was also thinking now that this could also be the cause of the original problem on your other issue regarding the AD4112 in continuous read mode. If the crystal oscillator failed to start after switching to external crystal and continuous read mode, then that could explain why /RDY initially pulses correctly after the reset, but fails to pulse after the write to MODE & IFMODE. The external crystal circuitry especially during start up is really sensitive on  any disturbances e.g. when supplying an SCLKs. Some of your later examples do not switch to a crystal and there should be no dependence on the Mux-selection regardless of clock-source. So might worth performing the same test while keeping the internal oscillator active instead. 

    I'll confirm this on my side and come back to you on this. 

    Thanks,

    Jellenie

Children
  • +1
    •  Analog Employees 
    on Jan 19, 2021 4:25 AM 2 months ago in reply to JellenieR

    Hi, 

    I confirmed that the caps C9 and C10 causes the issue. So if you can remove this on your end then that would probably solve the issue. It was an error in the BOM during the build I think as it supposed to be DNI in the first place.  

    However, on the other issues regarding the AD4111/12 boards, I also tried this on my board. It works fine using standard conversion mode. But I also experienced some issues switching with continuous read. I'm suspecting switching to external clock might have causes the issue because trying with internal oscillator works fine with continuous read mode. But I need to explore more about this to understand and verify the root cause. I'll let you know once I have an update on this. 

    Thanks,

    Jellenie

  • Thanks for figuring this out. For cost reasons, my plan is to use an external 8Mhz clock generated by the MCU for the AD4115. I hate having multiple clock sources on a board.

    BTW I found another quirk on the AD4115 when doing continuous reads on a single channel at 125KSPs. I'm using a SPI clock of 8Mhz and appending the status byte to the end of the reading. I have observed that the data looks correct but that the status byte has invalid values such as 0x3F, 0x7F, or 0xFF. I appear to have ample time between readings - RDY returns to the high state after the status byte. And if I I operate at 62.5KSPs everything works correctly.

  • 0
    •  Analog Employees 
    on Jan 24, 2021 3:14 PM 2 months ago in reply to WallyBalls

    Hi, 

    I've actually tried the continuous read mode on AD4111. It has the same circuitry and board as AD4112. And it works fine. RDY is pulsing at correct ODRs. The issue that I was talking about on the above reply is more on the Eval+ software bugs and it has nothing to do nor related to external crystal issue. The external crystal works fine. I'm planning to reply this to the other thread when I get a chance. 

    But on the AD4115, I haven't tried it. But I was thinking if you increase the SCLK frequency for example. Does it works fine? 

    Thanks,

    Jellenie