LMP91000

SNAS506H – JANUARY 2011 – REVISED MARCH 2013

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Bit

Name

Function

BIAS selection (Percentage of the source reference)

0000 0% (default)

0001 1%

0010 2%

0011 4%

0100 6%

0101 8%

[3:0]

BIAS

0110 10%

0111 12%

1000 14%

1001 16%

1010 18%

1011 20%

1100 22%

1101 24%

MODECN -- Mode Control Register (address 0x12)

The Parameters in the Mode register allow the configuration of the Operation Mode of the LMP91000.

Bit

Name

Function

Shorting FET feature

7

FET_SHORT

0 Disabled (default)

1 Enabled

[6:3]

RESERVED

Mode of Operation selection

000 Deep Sleep (default)

001 2-lead ground referred galvanic cell

[2:0]

OP_MODE

010 Standby

011 3-lead amperometric cell

110 Temperature measurement (TIA OFF)

111 Temperature measurement (TIA ON)

When the LMP91000 is in Temperature measurement (TIA ON) mode, the output of the temperature sensor is

present at the VOUT pin, while the output of the potentiostat circuit is available at pin C2.

GAS SENSOR INTERFACE

The LMP91000 supports both 3-lead and 2-lead gas sensors. Most of the toxic gas sensors are amperometric

cells with 3 leads (Counter, Worker and Reference). These leads should be connected to the LMP91000 in the

potentiostat topology. The 2-lead gas sensor (known as galvanic cell) should be connected as simple buffer

either referred to the ground of the system or referred to a reference voltage. The LMP91000 support both

connections for 2-lead gas sensor.

3-lead Amperometric Cell In Potentiostat Configuration

Most of the amperometric cell have 3 leads (Counter, Reference and Working electrodes). The interface of the 3-

lead gas sensor to the LMP91000 is straightforward, the leads of the gas sensor need to be connected to the

namesake pins of the LMP91000.

The LMP91000 is then configured in 3-lead amperometric cell mode; in this configuration the Control Amplifier

(A1) is ON and provides the internal zero voltage and bias in case of biased gas sensor. The transimpedance

amplifier (TIA) is ON, it converts the current generated by the gas sensor in a voltage, according to the

transimpedance gain:

If different gains are required, an external resistor can be connected between the pins C1 and C2. In this case

capacitance of the gas sensor acts as a low pass filter.

18

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