AD22151 Minimum Magnetic Field Strength

What is the minimum magnetic field strength in Gauss that the AD22151 can reliably measure considering noise sources and what gain would be appropriate?   The application would be a static magnetic field so a bandwidth below 50hz would be appropriate.   The  noise section of the data sheet indicates 1 mV rms noise with 5mV/G would give a a minimum detectable signal of 0.2 Gauss.  Can the AD22151 be used at this level of signal or lower and what would be the external circuit design considerations?   An update to the data sheet giving minimum detectable Gauss levels would be appropriate.

  • 0
    •  Analog Employees 
    on Feb 7, 2019 7:01 AM over 1 year ago

    Hi,

    Op amps' noise at low frequencies are generally higher. Filtering is one of the way to reduce the noise. The 1mVrms noise in the datasheet is true for 100Hz LP filter. For your application of 50Hz you can follow the approximate noise given on the datasheet. Set your cut-off frequency @100Hz to make sure that your frequency of operation is within the flat band. The minimum stable gain of the AD22151 is 2 meaning the lowest sensitivity it could get is 0.8mV/G. The sensitivity has always been a certain voltage per 1 Gauss, the gain is only altered depending on what range of magnetic field you want to measure and to maximize the sensor reading with regards to noise and temperature compensations. You would want your output be higher than the inate noise voltage your system has.

    Let me know if you need any clarifications.

    Regards,
    Goz

  • Hi Mr. Goz,

    we are working with AD22151 for a long time and only now we know that the minimum stable gain is 2!

    This is a giant problem for us, We have a lot of encoders where the pin 5 and pin 6 are connected together as follower amplifier.

    So, you confirm that we have to move to two resistance to have a gain of 2! There are different solution to stabilize the circuit?

    Let me know

    Regards

    Ing. Marco Gavesi

  • 0
    •  Analog Employees 
    on Nov 14, 2019 1:52 AM over 1 year ago in reply to marco_gavesi

    Hi Marco,

    No problem with a follower configuration. The gain of 2 is only needed maximize the use of the full output swing range. Please be minded that  in gain of 1 configuration the output won't swing to the either rail.

    Let me know if you have any clarifications.


    Best Regards,
    Goz


  • Hi Goz,

    what about the VREF output  (pin 7) ?  What is the output current capabilitty ouf this output?

    it is stable with 30 Kohm in parallel with 100 nF stable?

    Let me know

    Regards

    Marco

  • 0
    •  Analog Employees 
    on Nov 15, 2019 5:59 AM over 1 year ago in reply to marco_gavesi

    Hi Marco,

    Let me verify this on the lab. I'll get back to you.

    Regards,
    Goz