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LMP91000: 3 lead potentiostat amplifier specification

Robert Alfonsi
Prodigy 80 points
Part Number: LMP91000

What is the implication of the I(ce) minimum operating current capability of 750uA for the LMP91000 potentiostat circuit (ref. page 5 of LMP91000 spec)?

I want to use a gas sensor with a pretty low sensitivity, in 10's nA/ppm, and indeed page 1 of the spec invites you to use the device for very low sensitivity sensors "0.5nA/ppm", so how does this minimum operating current evidence itself in an environment when much lower current flows are expected to be seen within the sensor circuit?

Is this just the minimal level of internal current dissipation?

  • 0
    TI__Expert 5695 points
    The I(ce) current ratings are the for the control amplifier A1 and the function of this amplifier is explained in the section of the data sheet captured below:

    7.3.1.2 Control Amplifier
    The control amplifier (A1 op amp) has two tasks: a) providing initial charge to the sensor, b) providing a bias
    voltage to the sensor. A1 has the capability to drive up to 10 mA into the sensor in order to to provide a fast initial
    conditioning. A1 is able to sink and source current according to the connected gas sensor (reducing or oxidizing
    gas sensor). It can be powered down to reduce system power consumption. However powering down A1 is not
    recommended, as it may take a long time for the sensor to recover from this situation.

    The sensitivity of the sensor, on the other hand, is how small the cell current can be from the sensor. De[ending on how small l this current is (e.g. 10 nA) the TIA (trans-impendance amplifier) gain can be adjusted accordingly as explained on section 7.3.1 Potentiostat Circuitry of the data sheet.

    7.3.1.1 Transimpedance Amplifier
    The transimpedance amplifier (TIA) has 7 programmable internal gain resistors. This accommodates the full
    scale ranges of most existing sensors. Moreover an external gain resistor can be connected to the LMP91000
    between C1 and C2 pins. The gain is set through the I2C interface.

    Regards,
    Jose
  • 0 in reply to Jose Arteaga4
    Prodigy 80 points
    Hi & thanks Jose,
    I understand the purpose of the A1 amplifier & the TIA as you have explained above.
    Clearly the 10mA relates to the maximum current to source/sink from A1, but what is this 750uA "Ice minimum operating current capability relating to? What note should designers make of this point in the spec?
    regards
    Robert
  • 0 in reply to Robert Alfonsi
    TI__Expert 5695 points
    750 uA is the minimum operating current capability for sink and source conditions for the A1 amplifier.