Datasheet

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= e
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2
e
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+
2
e
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2
LMP2231
www.ti.com SNOSB01E –JANUARY 2008–REVISED MARCH 2013
APPLICATION INFORMATION
LMP2231
The LMP2231 is a single CMOS precision amplifier that offer low offset voltage and low offset voltage drift, and
high gain while only consuming 10 μA of current per channel.
The LMP2231 is a micropower op amp, consuming only 10 μA of current. Micropower op amps extend the run
time of battery powered systems and reduce energy consumption in energy limited systems. The ensured supply
voltage range of 1.8V to 5.0V along with the ultra-low supply current extend the battery run time in two ways. The
extended ensured power supply voltage range of 1.8V to 5.0V enables the op amp to function when the battery
voltage has depleted from its nominal value down to 1.8V. In addition, the lower power consumption increases
the life of the battery.
The LMP2231 has an input referred offset voltage of only ±150 μV maximum at room temperature. This offset is
ensured to be less than ±230 μV over temperature. This minimal offset voltage along with very low TCV
OS
of only
0.3 µV/°C typical allows more accurate signal detection and amplification in precision applications.
The low input bias current of only ±20 fA gives the LMP2231 superiority for use in high impedance sensor
applications. Bias Current of an amplifier flows through source resistance of the sensor and the voltage resulting
from this current flow appears as a noise voltage on the input of the amplifier. The low input bias current enables
the LMP2231 to interface with high impedance sensors while generating negligible voltage noise. Thus the
LMP2231 provides better signal fidelity and a higher signal-to-noise ration when interfacing with high impedance
sensors.
Texas Instruments is heavily committed to precision amplifiers and the market segment they serve. Technical
support and extensive characterization data is available for sensitive applications or applications with a
constrained error budget.
The operating supply voltage range of 1.8V to 5.5V over the extensive temperature range of −40°C to 125°C
makes the LMP2231 an excellent choice for low voltage precision applications with extensive temperature
requirements.
The LMP2231 is offered in the space saving 5-Pin SOT-23 and 8-pin SOIC package. These small packages are
ideal solutions for area constrained PC boards and portable electronics.
TOTAL NOISE CONTRIBUTION
The LMP2231 has a very low input bias current, very low input current noise, and low input voltage noise for
micropower amplifier. As a result, this amplifier makes a great choice for circuits with high impedance sensor
applications.
Figure 48 shows the typical input noise of the LMP2231 as a function of source resistance where:
e
n
denotes the input referred voltage noise
e
i
is the voltage drop across source resistance due to input referred current noise or e
i
= R
S
* i
n
e
t
shows the thermal noise of the source resistance
e
ni
shows the total noise on the input.
Where:
The input current noise of the LMP2231 is so low that it will not become the dominant factor in the total noise
unless source resistance exceeds 300 MΩ, which is an unrealistically high value. As is evident in Figure 48, at
lower R
S
values, total noise is dominated by the amplifier’s input voltage noise. Once R
S
is larger than a 100 kΩ,
then the dominant noise factor becomes the thermal noise of R
S
. As mentioned before, the current noise will not
be the dominant noise factor for any practical application.
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