LMP91000SDE/NOPB National Semiconductor, LMP91000SDE/NOPB Datasheet - Page 16

• Manufacturer Part Number: LMP91000SDE/NOPB
• Description: IC AFE INTERFACE 14-LLP
• Manufacturer: National Semiconductor

Specifications of LMP91000SDE/NOPB

• Number Of Channels: 1
• Voltage - Supply, Analog: 2.7 V ~ 5.25 V
• Voltage - Supply, Digital: 2.7 V ~ 5.25 V
• Package / Case: 14-WFDFN Exposed Pad
• Input Voltage: 5.25V
• Supply Current: 10µA
• Ic Output Type: Analog
• Sensor Case Style: QFN
• No. Of Pins: 14
• Supply Voltage Range: 2.7V To 5.25V
• Rohs Compliant: Yes
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Power (watts): -
• Number Of Bits: -
• Lead Free Status / Rohs Status: Compliant
• Other names: LMP91000SDE/NOPBTR

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MODECN -- Mode Control Register (address 0x12)
The Parameters in the Mode register allow the configuration of the Operation Mode of the LMP91000.
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, Refer-
ence 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.
[6:3]
[2:0]
Bit
7
FET_SHORT
RESERVED
OP_MODE
Name
Function
Shorting FET feature
0 Disabled (default)
1 Enabled
Mode of Operation selection
000 Deep Sleep (default)
001 2-lead ground referred galvanic cell
010 Standby
011 3-lead amperometric cell
110 Temperature measurement (TIA OFF)
111 Temperature measurement (TIA ON)
16
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 bi-
ased gas sensor. The transimpedance amplifier (TIA) is ON,
it converts the current generated by the gas sensor in a volt-
age, according to the transimpedance gain:
Gain=R
If different gains are required, an external resistor can be
connected between the pins C1 and C2. In this case the in-
ternal feedback resistor should be programmed to “external”.
The R
sensor acts as a low pass filter.
Load
TIA
together with the output capacitance of the gas