AD4112's VIN0~VIN7 measured voltage 200mV~500mV when no input signal.

AD4112's VIN0~VIN7 measured voltage 200mV~500mV when no input signal.
It's serious problem...
I don't know what's the problem.
my schematic is following :


what's wrong???

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  • 0
    •  Analog Employees 
    on Jul 31, 2019 6:55 AM

    Hi,

    What do you mean by no input signal? Is that mean you have a floating inputs? If you are measuring a floating inputs, well that's the problem. Or do you mean you have a differential input voltage of 0V and see this offset value? May I know how exactly did you measured this value? 

    Thanks,

    Jellenie 

  • Yes, 'no input singal' mean floating inputs. it's voltage come out from VIN0~VIN8.
    Everything okay when I connect voltage source on VINx and VINCOM.
    when make it floating, come out voltage about 200mV~500mV from VINx .

  • 0
    •  Analog Employees 
    on Jul 31, 2019 8:30 AM in reply to ManseungYoo

    Hi,

    Yes, you do not usually measure a floating inputs as the inputs are floating you do not know exactly what value are you trying to measure since it could float to any value. Why do you have to measure it anyway? May I know what is your application? If you are bothered with floating inputs, It would be best to connect it to GND when unused to ensure that it will stay at a known level and within specified input range.  

    Thanks,

    Jellenie

  • My application is DDC(Direct Digital Controller), AD4112 be used at Analog Input 8ch.

    Generally, it is connected with voltage source from voltage type sensor on the input side.
    However, if there is no connection, does it should be 0v cause pull-down 100k resistor(R206)?



    but VIN0's voltage be measured by oscilloscope,
    and AD4112's AD conversion result also return it's value.

    It is not possible to judge whether the sensor is not connected or the sensor's wiring is opened.

    Is the 100kohm pull-down resistor's value  is too large?

Reply
  • My application is DDC(Direct Digital Controller), AD4112 be used at Analog Input 8ch.

    Generally, it is connected with voltage source from voltage type sensor on the input side.
    However, if there is no connection, does it should be 0v cause pull-down 100k resistor(R206)?



    but VIN0's voltage be measured by oscilloscope,
    and AD4112's AD conversion result also return it's value.

    It is not possible to judge whether the sensor is not connected or the sensor's wiring is opened.

    Is the 100kohm pull-down resistor's value  is too large?

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