AD7795 External Clock

In single conversion mode the AD7795 powers up takes a conversion then returns to the power down mode. I presume the internal clock is stopped during power down mode.

I want to drive the ADC with an accurate microcontroller derived 128Khz clock for better immunity and synchronisation of multiple devices using the external clock divide by 2 option.

1) Do I need to stop the clock when I have read the conversion ?

2) Do I need to stop the clock when I read the conversion to get the same power down current as when using an internal clock.

3) Are there any side effects of stopping the external clock between conversions. Presumably the 1ms clock stabilisation time with the internal clock is not required with an external clock.

  • 0
    •  Analog Employees 
    on Dec 17, 2015 11:21 PM

    Hi, Patrick.

    Sorry for late response. I think the ADC has the same consumption in shutdown mode regardless of using internal or external clock. If you are concern with the system current consumption, you can stop the clock during ADC's power down mode. However, make sure that you provide the clock during ADC's normal operation and the external clock provided are within the specs to avoid any issues or side effects. You may also consider using the internal clock of one ADC and supply it to others ADC for synchronization of multiple devices.

    Thanks,

    Jellenie

  • Hi Jellenie

    Thanks for your answer. I already use the method you describe; using one internal clock to drive the others for sync. The external clock is crystal controlled and should give better mains immunity.

    Pat

  • 0
    •  Analog Employees 
    on Jan 10, 2016 7:11 PM

    Hi, Pat.

    Yes, external clock can be more accurate since it can be accurately controlled than the internal clock which is trimmed within a specified accuracy of +/-3% for AD7795. Using the internal clock lessen the need for external clock circuit and helps you minimize the board size and cost. It really depends on your application if the internal clock accuracy is sufficient in your application or you really need a more accurate external clock circuit.

    Thanks,

    Jellenie

  • 0
    •  Analog Employees 
    on Aug 2, 2018 3:18 PM
    This question has been assumed as answered either offline via email or with a multi-part answer. This question has now been closed out. If you have an inquiry related to this topic please post a new question in the applicable product forum.

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