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Original question:

LMP91000: Bias voltage settings for LMP91000 at 200mV

LMP91000: Clarification of previous thread

Brian Inman
Prodigy 10 points
Part Number: LMP91000


Ok, I'm reading the "LMP91000: Bias voltage settings for LMP91000 at 200mV", (https://e2e.ti.com/support/sensors-group/sensors/f/sensors-forum/1077550/lmp91000-bias-voltage-settings-for-lmp91000-at-200mv) and it has me a bit confused.

From Gordon Varney:

---

Remember the CE pin is set to your reference voltage not your bias voltage. If you measure from CE to GND you will measure your reference voltage divided by the selected percentage. by default it is 50% of VDD = 1.65Vdc.

Your bias voltage is between CE and RE not ground

Confirmed, Internal Reference, Zero = 20% (3.3V * 0.2 = 0.66V), Bias polarity = positive, Bias = 0.06% (3.3V * 0.06 = 0.198V), Shorting FET = Disabled, Mode = 3-lead amperometric cell. 

---

So, In this configuration, I would expect: 

CE = 0.66V

RE = 0.858V

Is this correct?

My confusion comes from the measurements posted in the above thread, as well as:

Which references WE & RE, not CE & RE.

I appreciate the clarification.

Thanks,

   Brian

  • 0
    TI__Genius 9380 points

    Brian,

      The WE - RE reference is the polarity. How the current of the probe moves relative to the CE pin. CE sets your Zero. WE-RE determine if the probe current is positive or negative. 

    If CE is 0.66 and RE is 0.858 and the polarity is negative it becomes 0.66-0.858 = -0.198

  • 0 in reply to Gordon Varney
    Prodigy 10 points

    Gordon,

    I understand the polarity is based on CE - RE.  

    With the settings given

    Internal Reference, Zero = 20% (3.3V * 0.2 = 0.66V), Bias polarity = positive, Bias = 0.06% (3.3V * 0.06 = 0.198V), Shorting FET = Disabled, Mode = 3-lead amperometric cell. 

    Is the RE 0.858 or 0.462? or ... something else?

    Thanks,

       Brian

  • 0 in reply to Brian Inman
    TI__Genius 9380 points

    Brian,

      It depends on your polarity. The probe is based on a current, the current can be positive or negative. CE is your zero. Based on the probe the voltage developed can be above or below the zero.