30132583
FIGURE 4. 3-Lead Amperometric Cell
2-lead Galvanic Cell In Ground Referred Configuration
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.
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 gain of this non inverting amplifier is set according the
following formula
Gain= 1+(RTIA/RLoad
)
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 LMP91000 is then configured in 2-lead galvanic cell
mode and the Vref bypass feature needs to be enabled. In
17
www.ti.com
TI [ TEXAS INSTRUMENTS ]
