AD5342, question on reference input

Hi,

 

Please let me ask what is impedance value of reference input(VrefA and VrefB) of AD5342, when it is not powered ?

 

We are now studying one issue of our board, and it seems reference input is powered before the part is powered. To understand what is occured, we would like to know the value of impedance.  BUF pin is connected to +3.3V, but it should be 0V by connected to GND when it is not powered.

 

Thank you very much for your support,

 

Best Regards,

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  • 0
    •  Analog Employees 
    on Apr 29, 2014 9:52 AM

    Hi Usaghi,

    the input reference pin is internally protected by ESD diodes.

    If the part is not powered, the protection diodes will clamp the voltage to Vdd - 0.3V...

    Vdd is not powered but probably connected to a supply so.. two things may happen,

    1- the supply is at high impedance, then teh part is powered indirectly by the reference.

    2-the supply is at low impedance, then the reference is probably short- circuited to gnd.

    Regards,

    Miguel

Reply
  • 0
    •  Analog Employees 
    on Apr 29, 2014 9:52 AM

    Hi Usaghi,

    the input reference pin is internally protected by ESD diodes.

    If the part is not powered, the protection diodes will clamp the voltage to Vdd - 0.3V...

    Vdd is not powered but probably connected to a supply so.. two things may happen,

    1- the supply is at high impedance, then teh part is powered indirectly by the reference.

    2-the supply is at low impedance, then the reference is probably short- circuited to gnd.

    Regards,

    Miguel

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