LMP7721 Datasheet, PDF (1/16 Pages) National Semiconductor (TI) – 3 Femtoampere Input Bias Current Precision Amplifier

March 14, 2008
LMP7721
3 Femtoampere Input Bias Current Precision Amplifier
General Description
The LMP7721 is the industry’s lowest guaranteed input bias
current precision amplifier. The ultra low input bias current is
3 fA, with a guaranteed limit of ±20 fA at 25°C and ±900 fA at
85°C. This is achieved with the latest patent pending tech-
nology of input bias current cancellation amplifier circuitry.
This technology also maintains the ultra low input bias current
over the entire input common mode voltage range of the am-
plifier.
Other outstanding features, such as low voltage noise (6.5
nV/ ), low DC offset voltage (±150 µV maximum at 25°C)
and low offset voltage temperature coefficient (−1.5 µV/°C),
improve system sensitivity and accuracy in high precision ap-
plications. With a supply voltage range of 1.8V to 5.5V, the
LMP7721 is the ideal choice for battery operated portable ap-
plications. The LMP7721 is part of the LMP^® precision am-
plifier family.
As part of National’s PowerWise^® products, the LMP7721
provides the remarkably wide gain bandwidth product (GBW)
of 17 MHz while consuming only 1.3 mA of current. This wide
GBW along with the high open loop gain of 120 dB enables
accurate signal conditioning. With these specifications, the
LMP7721 has the performance to excel in a wide variety of
applications such as electrochemical cell amplifiers and sen-
sor interface circuits.
The LMP7721 is offered in an 8-pin SOIC package with a
special pinout that isolates the amplifier’s input from the pow-
er supply and output pins. With proper board layout tech-
niques, the unique pinout of the LMP7721 will prevent PCB
leakage current from reaching the input pins. Thus system
error will be further reduced.
Features
Unless otherwise noted, typical values at T_A = 25°C, V_S = 5V.
■ ^{Input bias current (V}_CM ^{= 1V)}
— max @ 25°C
±20 fA
— max @ 85°C
±900 fA
■ ^{Offset voltage}
±26 µV
■ ^{Offset voltage drift}
−1.5 μV/°C
■ ^{DC Open loop gain}
120 dB
■ ^{DC CMRR}
100 dB
■ ^{Input voltage noise (at f = 1 kHz)}
6.5 nV/√Hz
■ ^THD
0.0007%
■ ^{Supply current}
1.3 mA
■ ^GBW
17 MHz
■ ^{Slew rate (falling edge)}
12.76 V/μs
■ ^{Supply voltage}
1.8V to 5.5V
■ ^{Operating temperature range}
−40°C to 125°C
■ ^{8-Pin SOIC}
Applications
■ ^{Photodiode amplifier}
■ ^{High impedance sensor amplifier}
■ ^{Ion chamber amplifier}
■ ^{Electrometer amplifier}
■ ^{pH electrode amplifier}
■ ^{Transimpedance amplifier}
Block Diagram of a Typical Application
Ion Chamber: Current to Voltage Converter
LMP^® is a registered trademark of National Semiconductor Corporation.
PowerWise^® is a registered trademark of National Semiconductor.
© 2008 National Semiconductor Corporation 202040
20204084
www.national.com