LMP7721

SNOSAW6E – JANUARY 2008 – REVISED DECEMBER 2014

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7 Detailed Description

7.1 Overview

The LMP7721 combines a patented input bias current cancelling circuitry along with an optimized pinout to

provide and ultra-low maximum specified bias current of ±20 fA.

7.2 Functional Block Diagram

7.3 Feature Description

7.3.1 Ultra-Low Input Bias Current

The LMP7721 has the industry’s lowest specified input bias current. The ultra-low input bias current is typically 3

fA, with a specified limit of ±20 fA at 25°C, ±900 fA at 85°C and ±5 pA at 125°C when VCM = 1 V with a 5-V or a

2.5-V power supply.

7.3.2 Wide Bandwidth at Low-Supply Current

The LMP7721 is a high-performance amplifier that provides a 17-MHz unity gain bandwidth while drawing only

1.3 mA of current. This makes the LMP7721 ideal for wideband amplification in portable applications.

7.3.3 Low Input Referred Noise

The LMP7721 has a low input-referred voltage noise density (6.5 nV

at 1 kHz with 5-V supply). Its MOS input

stage ensures a very low input-referred current noise density (0.01 pA/

).

The low input-referred noise and the ultra-low input bias current make the LMP7721 stand out in maintaining

signal fidelity. This quality makes the LMP7721 a suitable candidate for sensor-based applications.

7.3.4 Low-Supply Voltage

The LMP7721 has performance specified at 2.5-V and 5-V power supplies. The LMP7721 is ensured to be

functional at all supply voltages between 2 V to 5.5 V, for ambient temperatures ranging from

−40°C to 125°C.

This means that the LMP7721 has a long operational span over the battery's lifetime. The LMP7721 is also

specified to be functional at 1.8-V supply voltage, for ambient temperatures ranging from 0°C to 125°C. This

makes the LMP7721 ideal for use in low-voltage commercial applications.

7.3.5 Rail-to-Rail Output and Ground Sensing

Rail-to-rail output swing provides the maximum possible output dynamic range. This is particularly important

when operating at low-supply voltages. An innovative positive feedback scheme is created to boost the

LMP7721’s output current drive capability. This allows the LMP7721 to source 30 mA to 40 mA of current at 1.8-

V power supply.

The LMP7721’s input common-mode range includes the negative supply rail which makes direct sensing at

ground possible in single-supply operation.

16

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