ADCMP572 VTT pin confusion

We've received 2 ADCMP572 eval boards, but unfortunately the documentation for the part and the eval board seems to be inconsistent.

As a result, I have a question:  should VTT (pin 8) be tied to GND or pulled high? 


Per the part datasheet (pg. 6) it should be tied to VCCO, but on the eval board it is jumpered to the ground plane (APLANE) via P3, and that is listed as being the correct jumper setting (pg. 9).

  Thanks.

  • Hi rmauro-

    I checked with an apps engineer here on this and he provided me with the following information:

    The VTT pin 8 should be connected to Vcco as stated in the datasheet.  For the evaluation board application the power supplies have been shifted down such that Vcco is at 0V or ground.

    As such, the Vtt pin is correctly connected via Jumper P3 to ground, which is Vcco.  Please note that Cgnd is at -3.3V.  The ADCMP572 power supplies can be shifted in voltage, keeping the Vcco to ground voltage differential as called out in the specification.  The reason for shifting the power supplies is that most of the digital sampling scope inputs are 50ohms to ground.  By shifting the power supplies, you can directly connect the comparator’s output to a 50 ohm to ground input on a sampling scope while maintaining the correct termination voltage required by the comparator outputs to operate correctly.  

    I hope this helps.

    Regards,

    AndyR

    EngineerZone Support Community Manager

  • Thanks.

     

    Rob Mauro

    Field Applications Engineer

    ARROW ELECTRONICS

    90 East Halsey Road

    Parsippany,  NJ  07054

    Cell: 732-859-8994

     

     

     

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  • 0
    •  Analog Employees 
    on Aug 2, 2018 4:50 PM over 2 years ago
    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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    EZ Admin