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    AD8428 output offset problem

    Hi, i use AD8428. +V 4.99V and -V 5.01V if i not connect anythink to +/- input, i see -0.06V from output . If i connecto all input to GND this time i see 24mv from output of AD8428. How can i set offset output voltage ?

    Thank u

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    Re: AD8428 output offset problem

    When compared to the datasheet the offset voltage which you are getting is very high. Better check for the noises in the ground and try to eliminate it. Use a stable DC voltage to power the instrumentation amplifier.Noise on the supply pins can adversely affect performance.

    Place a 0.1 μF capacitor as close as possible to each supply pin. Because the length of the bypass capacitor leads is critical at high frequency, surface-mount capacitors are recommended. Parasitic inductance in the bypass ground trace works against the low impedance created by the bypass capacitor. a 10 μF capacitor can be used farther away from the device. For larger value capacitors, which are intended to be effective at lower frequencies, the current return path distance is less critical. In most cases, the 10 μF capacitor can be shared by other precision integrated circuits.
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    Re: AD8428 output offset problem

    I added 100nf,10nf,1nf and 10uf capacitor each voltage input. But output voltage is same. I think add resistor Vin+ and Vin- is useful ?



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    Re: AD8428 output offset problem

    Hi,

    show your circuit please.

    if i not connect anythink to +/- input
    --> this means floating. DON´T let inputs floating. This measurement makes no sense!

    *****
    If i connecto all input to GND this time i see 24mv from output of AD8428.
    according datasheet you can calculate with max. 25uV input ofsset current.
    --> multiply this with your gain of 2000 then you may expect 50mV output offfset voltage. You see 24mV --> this is within specification.

    Klaus



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    Re: AD8428 output offset problem

    Klaus mentions a gain of 2000. I don't see your circuit's gain mentioned in your post...perhaps it was edited out?

    What is your circuit's gain? What value resistors are you using? Share your circuit please!
    Very high valued resistors require that the + and - inputs see a balanced resistance, otherwise Ios may produce an undesirable voltage offset.
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    Re: AD8428 output offset problem

    AD8428 has fixed gain 2000. I didnt use any resistor in input . I connected sensor directly.

    My schematic pdf link.
    https://www.dropbox.com/s/alfm3hmsvz...C_Arm.pdf?dl=0



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    Re: AD8428 output offset problem

    Hi,

    This is an instrumentation amplifier.
    Both inputs are the same high impedance.
    I see a 10M at the IN+, but none on the IN-.
    Usually both inputs should be treated the same, therefore i recommend to connect a 10M to the IN- too.

    Klaus



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