eni =

en +

2

ei +

2

et

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 TCVOS 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:

en denotes the input referred voltage noise

ei is the voltage drop across source resistance due to input referred current noise or ei = RS * in

et shows the thermal noise of the source resistance

eni 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 M

Ω, which is an unrealistically high value. As is evident in Figure 48, at

lower RS values, total noise is dominated by the amplifier’s input voltage noise. Once RS is larger than a 100 kΩ,

then the dominant noise factor becomes the thermal noise of RS. As mentioned before, the current noise will not

be the dominant noise factor for any practical application.

Copyright © 2008–2013, Texas Instruments Incorporated

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