LMP91000SDE National Semiconductor, LMP91000SDE Datasheet - Page 17

• Manufacturer Part Number: LMP91000SDE
• Description: AFE, SENSOR, 14LLP
• Manufacturer: National Semiconductor

Specifications of LMP91000SDE

• Brief Features: Programmable Cell Bias Voltage, Low Bias Voltage Drift, I2C Compatible Digital Interface
• Supply Voltage Range: 2.7V To 5.25V
• Operating Temperature Range: -40°C To +85°C
• Digital Ic Case Style: LLP
• Ic Function: Programmable Analogue Front End (AFE)
• Rohs Compliant: Yes
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

2-lead Galvanic Cell In Ground Referred Configuration
When the LMP91000 is interfaced to a galvanic cell (for in-
stance to an Oxygen gas sensor) referred to the ground of the
system, an external resistor needs to be placed in parallel to
the gas sensor; the negative electrode of the gas sensor is
connected to the ground of the system and the positive elec-
trode to the Vref pin of the LMP91000, the working pin of the
LMP91000 is connected to the ground.
The LMP91000 is then configured in 2-lead galvanic cell
mode and the Vref bypass feature needs to be enabled. In
FIGURE 4. 3-Lead Amperometric Cell
17
this configuration the Control Amplifier (A1) is turned off, and
the output of the gas sensor is amplified by the Tran-
simpedance Amplifier (TIA) which is configured as a simple
non-inverting amplifier.
The gain of this non inverting amplifier is set according the
following formula
Gain= 1+(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”.
TIA
/R
Load
)
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