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LM4051-N: Precision current source for Hall sensor

Chris van der Aar
Intellectual 570 points
Part Number: LM4051-N
Other Parts Discussed in Thread: LM4041-N, REF50E, REF35

Tool/software:

For flux sensor mesuerements we want to use a Hall sensor where we need a constant current source of 2mA.
The manufacturer of the Hall sensor describes the circuit below for offset compensation. The sensor needs a constant current of 2mA.

Maybe you can give us some suggestions about the current source that can be used (e.g. LM4051?) and the instrumentation opamp and the output opamp shown in the circuit below? Or maybe a reference design with a hall sensor? We prefer a differential analog output for minimizing noise because it has to be connected with a measurement circuit (probably with a differential analog input but we have to select something  for that).

The Hall sensor output is 200mV max (positive or negative) for the Hall sensor we are using. The output should be around 5V max I expect (depending on the controller/measuring system we are going to use but this is still under investigation)

  • 0
    TI__Expert 5620 points

    Hello,

    There are a few options to create a current source. LM4051AIM3X-ADJ/NOPB (LM4051-N) or LM4041CEM3X-ADJ/NOPB (LM4041-N) are good options to do so. An example using one of these devices can be seen in section 3.2 of this application note:

    https://www.ti.com/lit/an/snoaa46/snoaa46.pdf 

    For increased accuracy, you could consider a configuration as described in section 3.3 of the application note, using a series voltage reference, such as REF35 or REF50E:

    I will let the op-amp experts comment on which amplifier is best to use here. 

    Thanks,

    Jackson

  • 0 in reply to Jackson Wightman
    TI__Guru**** 151256 points

    Chris,

    What are the supply voltages available?

  • 0 in reply to Ron Michallick
    Intellectual 570 points

    I gueess +24V from the system but in fact I can make any voltage with a low noide LDO when the current consumption remains low. Or otherwise a low noise converter. I have some examples already from T.I.

  • 0 in reply to Chris van der Aar
    TI__Guru**** 151256 points

    Chris,

    Does the processed linear output voltage go an ADC or another linear circuit?

    I'll assume ADC below, for now using 5V supply and ADC reference. 

    This uses OP1 and NMOS to make a typical current (based on VCC). Use VCC as the ADC reference to cancel error in VCC voltage.
    After the hall, INA can amplify then signal goes to a single ended (hall up to +/-200mV = [0.5V to 4.5V]) or difference ADC input [-2V to 2V].  

    Another option is to mirror the VCC to hall current.  This changes the VCM for OPA and INA. Otherwise it works the same 

    Of course the INA needs to work with the VCM and output range.

    On the other hand; If the next stage is also linear, then a precision reference should be used for 2mA generation and any other linear translation or comparison.