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LMP91002: Output Voltage

Drew Doran
Prodigy 240 points
Part Number: LMP91002
Other Parts Discussed in Thread: LMP91000

Hi,

I have a customer with the following question that I was hoping you could help me answer:

                "I am working in a new design with the LMP91002.  I was wondering if you would know whether the output of the sensor connected to the LMP91002 is riding on top of the Vrefx selected? or if the LMP91002 output is a full swing of the EC sensor connected to it?.

In other words, does the LMP91002 output varies from 0 to Vcc when gas is varied from 0 to the maximum concentration allowed by the EC sensor? Or the LMP91002 output varies from a Vrefx to Vcc when gas is varied from 0 to the maximum concentration allowed for the EC sensor?

Is there any way to measure the Vrefx?"

Thanks and regards,
Drew

  • 0
    TI__Expert 5695 points
    TI support team will contact you shortly.
  • 0 in reply to Jose Arteaga4
    TI__Prodigy 240 points

    Ok thanks! My customer followed up with a couple other questions I was hoping you could help me with as well:

    1) Where are the commands (instruction sets) for the LMP91002 and LMP91000

    2) Do you have any more information about the EC sensor health status check?

    Thanks and regards,
    Drew

  • 0
    TI__Expert 5145 points
    Hi Drew,

    The LMP91002 output voltage is equal to:

    Vout = Vref - Iw * RTIA

    The LMP91002 output range is from 0V to Vref, if the current is outgoing from the working electrode, or is from Vref to Vdd, if the current is incoming in the working electrode.

    Please let me know if this answer to your question.
    Best regards,
    Carmine
  • 0 in reply to Drew Doran
    TI__Expert 5145 points
    Hi Drew,

    1) you can program the LMP91000 and the LMP91002 through I2C serial interface. The register map with the explanation of the registers, is reported in the product datasheets (pag.14 for the LMP91002, pag. 21 for the LMP91000).

    2) No, sorry. You should refer to the EC sensor supplier.

    Best regards,
    Carmine
  • 0 in reply to Carmine Iascone
    TI__Prodigy 240 points

    Hi Carmine,

    Thank you for your answers. My customer has a couple of followup questions that I was hoping you could clarify as well:

                    "If I am not mistaken the Vref your contact is referring is the “virtual ground” from where the output voltage will vary depending on my gas concentration.  That is a critical distinction because I am feeding the same Vref I was using for my ADC into the LMP91002.  I can vary the “internal zero” through the REFCN register (but I only have three choices: 20%, 50% and 67%). 

    Is that “internal zero selection” voltage available externally?  (for example if I measure the C1, pin 10)  I know that voltage is a percentage (20%, 50% and 67%) but I’d like to feed it back to my –Vref ADC input (negative external reference).

                    Just in case, for clarification, when the datasheet on page 15 (section 7.6.4 REFCN Register) said 20% for the internal zero, when I am applying 2.5V as Vref to the LMP91002, then I get a internal zero of 0.5V, is that right?  My output will be varying from 0.5 V depending on the amount of gas (as your college said, 0.5V is the “Vref” from where: “output range is from 0V to Vref, if the current is outgoing from the working electrode, or is from Vref to Vdd, if the current is incoming in the working electrode”)

                    If I cannot measure directly the internal zero voltage, then I presume I can feed 0.5 V to my -Vref, is this right? (I am assuming my sensor voltage will be above 0.5 V (since they are zero bias, the H2S sensor should output a positive voltage above the internal zero)

                    The “diagnostic” health status I needed to access is also in REFCN register, so it looks like I have to applied it and then remove it. Can I applied a step different from 1%?  If I send DIAGNOSTIC = “000Ah” will I get a step of 10%?  I wonder if this step voltage is a parameter that I can play with to perform different studies on the EC sensor.

                    Any suggestion is appreciated."

     

    Thanks!

    Regards,
    Drew