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ADS7853: what situations can the value of CFR change the default value?

Lian Wu
Genius 5250 points
Part Number: ADS7853

Dears:

Recently we test our board with ADS7853, and find the value of CFR changed from 16'h8A40 to 16'h0000 when our board is 

Then the output of SDO_A/B is '0' level.

what situations can the value of CFR change the default value?

Thanks a lot!

Best regards

Luck Wu

  • 0
    TI__Guru 53516 points
    Hi Lian,

    The Configuration register is by default 0x0000h at power-up. The device will reset every time the power supply is cycled. Also a glitch in the supply or brownout condition could trigger a power-on-reset, returning the CFR register to default.

    Please let me know if you have questions,

    Thank you,

    Kind Regards,
    Luis
  • 0 in reply to Luis Chioye
    Prodigy 30 points
    Whether the input analog level super range will cause the reset？
    Is it usually configure CFR/REFDAC registers only after power on?
    To solve the abnormal reset of CFR/REFDAC registers, I need AD sampling to configure CFR registers at the same time.
    Is this method feasible?

    Thanks a lot!

    Best regards
    Wang He(friend of Luck)
  • 0 in reply to user4234764
    TI__Guru 53516 points

    Hi Wang,

    The analog input voltage level at the ADC inputs does not play a role in resetting the configuration registers. However, the input voltage levels must always remain between GND-0.3V to AVDD+0.3V or damage to the device may occur as shown of the Absolute Maximum Ratings Table on p.5 of the datasheet. The AVDD and DVDD voltage must remain stable.  The device only will reset the CFR registers if the supply power is cycled, or in a brownout event, where a glitch on the supplies could trigger the device to perform a Power-on reset; or when the user re-writes the CFR registers

    I am not sure I understand the last question. please clarify what you mean by: "To solve the abnormal reset of CFR/REFDAC registers, I need AD sampling to configure CFR registers at the same time. Is this method feasible".   

    Thanks and Regards,

    Luis

  • 0 in reply to Luis Chioye
    TI__Guru 53516 points
    HI Wang,

    Please let me know if you have additional questions,

    Kind Regards,
    Luis
  • 0 in reply to Luis Chioye
    Prodigy 30 points
    HI Luis
    ADS7853 still has a random reset problem,
    To solved the problem,I use two methods:
    A:I configuring CFR registers at the same time for AD_data sample.

    B:I'm sure it's the external interference that causes its reset.
    ADS7853 just only one GND,But our PCB has AGND and DVDD,
    I use a BL connect them at a point,the reset problem still exist;
    When I use a 0Ω-resistance to connect them,the reset problem Non-existent.

    So I want to know :
    A:Whether the method A is correct?
    B:The correct method to solve the two GND problem.


    Thanks a lot!

    Best regards
    Wang He
  • 0 in reply to user4234764
    TI__Guru 53516 points

    HI Wang,

    The CFR registers should not reset under normal conditions unless a POR occurs due to a brownout condition.   As you have mentioned, it is possible that a potential is forming between AGND and DGND on the PCB, and therefore, a brownout condition may be occurring due to GND bounce.   It is important that the device AVDD, DVDD and both the analog and digital signals are stable, referred to the same GND potential.  

    The ADS7853EVM board layout uses a single solid GND plane underneath the device.  The analog signals are routed on the left side of the board, and the digital on the right side.  However, some designers choose to split the DGND and AGND below of the A to D converter.  Regardless if you decide to use split digital and analog GND planes; or use a single GND plane for both digital and analog, the general recommendation is to route the sensitive analog input signals and reference signals away from the digital signals.  When using split GND planes, the digital and analog ground planes must remain at the same potential, and for this reason using the 0Ω-resistance to connect them may be the best.  Please let me know if you would like us to review your schematic.   You may find more information about different PCB board layout techniques and GROUND plane questions on the link below.

    Thank you,

    Kind Regards,

    Luis Chioye

    http://e2e.ti.com/support/data_converters/precision_data_converters/w/design_notes/1393.aspx

     

     

     

  • 0 in reply to Luis Chioye
    Prodigy 30 points

    HI Luis

    I tried to use 0Ω-resistance to connect them several days,The frequency of CFR reset reduced a lot. But,the CFR reset still appeared.

    So,I need your help to check the schematic.ADS7853_RESET.zip

    Thank you,

    Kind Regards,

    HE WANG

  • 0 in reply to user4234764
    TI__Guru 53516 points
    Hi Wang,

    In general, you want to ensure that the GND planes stay at the same potential.

    Since replacing L1 with a 0Ω-resistor to connect AGND and DGND reduced the frequency of the brownout event resetting registers , the issue is very likely due to a potential developing between the GND planes after a transient; or between the analog +5V and +A5V supplies

    The L1 connection does not show in the layout file plot provided. You could attempt improving the connection between the GND planes, by placing the connection between AGDN and DGND closer to the ADS7853; or reducing the impedance between them. Another possible suggestion, is to still split the layout into analog and digital sections, keeping the sensitive analog way from noise sources, but use a single GND plane underneath all devices.

    Best Regards,
    Luis