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LMP91000: LMP91000/LMP91002 Input Current range

Ebin Abraham
Prodigy 10 points
Part Number: LMP91000
Other Parts Discussed in Thread: LMP91002

What is the input current range support on the Working electrode of LMP91000/LMP91002? What must be the sensor's minimum and maximum current rate?

  • 0
    TI__Genius 9310 points

    Ebin,

      The LMP91000 generates an output voltage proportional to the cell current. Transimpedance gain is user programmable through an I 2C compatible interface from 2.75 kΩ to 350 kΩ making it easy to convert current ranges from 5 µA to 750 µA full scale. I hope this answers your question.

  • 0 in reply to Gordon Varney
    Prodigy 10 points

    Hi Mr Varney,

    Thanks for the reply. I confused this sentence in the datasheet

    "supports gas sensitivities over a range of 0.5 nA/ppm to 9500 nA/ppm. It also allows for easy conversion of current ranges from 5 μA to 750 μA full scale"

    Here what will be the minimum current it can detect? Is it 0.5nA or 5uA? And what is the highest current it can take 9500nA or 750uA? I know I misunderstood the above description. Would you mind explaining it to me?

  • 0 in reply to Ebin Abraham
    TI__Genius 9310 points

    Ebin,

      The LMP91000 supports Chemical Cells gas sensitivities over a range of 0.5 nA/ppm to 9500 nA/ppm. It also allows for an easy conversion of current ranges from 5 µA to 750 µA full scale.

    The load cell current for the TIA conversion is used to convert a voltage drop across the cell into a current. The current range of the TIA is 5ua to 750uA used for measuring. This is the measurement range of the TIA. The sensitivity of the measurement is 0.5 nA per PPM or part per million to 9500 nA/PPM. One current is the CE to WE current range of the measurement, the other is the current in nA per PPM of resolution. This tells you how sensitive the LMP91000 is to the gas change in the cell. You will have to select the load and gain settings to get the sensitivity you need for your gas call.  The last item is the load current on the CE of the cell. This is the bias current that makes the probe function. 

    The bias current, the load cell current for the TIA conversion and the sensitivity current are all different current specifications for using the LMP91000.

  • 0 in reply to Gordon Varney
    Prodigy 10 points

    Hi Mr Varney,

    Please correct me if I don't understand you correctly. So basically it was a test condition used in TIA. And starting from 5uA with a change of 0.5nA. Am I right?

    One more thing if you don't mind. Please find our sensor specification below. The sensor output current is 65 ± 25 nA/ppm. And it is a 200ppm sensor gives 18uA. But maximum overload is 500ppm gives a maximum 45uA current. So does this IC suitable for the application?

    Complete sensor's Specification:

    Output current: 65 ± 25 nA/ppm

    Nominal Range 0 - 200 ppm

    Maximum Overload 500 ppm

    Rec. Load Resistor: 10 - 33 Ω

    Bias (V_Sens-V_Ref): Not recommended

  • 0 in reply to Ebin Abraham
    TI__Genius 9310 points

    Ebin,

      Your assumption that the minimum current starting at 5uA would be able to see a 0.5nA change in the probe is correct. 

    Without knowing the part number of the cell you are considering it would be hard to say with absolute certainty that it will work, however with the data you have provided it does look like it will work. Remember setting up the LMP91000 require some knowledge of how gas sensing works as well a good understanding of how a TIA works. Do some reading and research, but I feel as though you will pick it up fast. Good Luck. 

  • 0 in reply to Gordon Varney
    Prodigy 10 points

    Thanks a lot. You have been very much helpful. I do appreciate it. Please share if you know any material to read about it. Thank you so much again.

  • 0 in reply to Ebin Abraham
    TI__Genius 9310 points

    Ebin,

      You are welcome. I find google to be a valuable resource. Start with TIA or transimpedance amplifiers.