Datasheet

LMP91000
SNAS506H –JANUARY 2011–REVISED MARCH 2013 www.ti.com
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:
Gain=R
TIA
If different gains are required, an external resistor can be connected between the pins C1 and C2. In this case
the internal feedback resistor should be programmed to “external”. The R
Load
together with the output
capacitance of the gas sensor acts as a low pass filter.
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