National Semiconductor Introduces Low Input Bias Current Amplifier

Santa Clara, CA - National Semiconductor Corp. recently introduced the LMP7721, a precision amplifier with the company's lowest guaranteed input bias current (20 fA) at room temperature and over the extended temperature range of -40 degrees to 125 degrees C. The device yields maximum system sensitivity and accuracy from photodiode and high-impedance sensors and is well-suited for improving sensitivity and accuracy in battery-operated portable applications, as well as electrochemical sensor interface circuitry. As a member of National's PowerWise family of energy-efficient products, the LMP7721 provides a wide gain bandwidth (GBW) of 17 MHz while consuming only 1.3 mA of current.

Compared to competitive amplifiers that suffer an exponential increase of input bias current over higher temperatures, National's proprietary VIP50 BiCMOS process technology enables the LMP7721's input bias cancellation circuitry to maintain its low input bias current. For example, the LMP7721 guarantees 900 fA at 85 degrees C, which is 50 percent less than the closest competitive device. Additionally, National provides a signal path solution for high-precision applications: Analog-to-digital converters (ADCs) such as the 12-bit ADC121S021 and 14-bit ADC141S626 are optimized to work with the LMP7721.

The LMP7721 precision amplifier provides 3 fA, with a guaranteed limit of 20 fA at 25 degrees C, 900 fA at 85 degrees C and 5 pA at 125 degrees C. The amplifier also maintains ultra low input bias current over its entire input common-mode voltage range, and its wide GBW along with high open-loop gain of 120 dB enables accurate signal conditioning. Additional features of the LMP7721 include low input voltage noise of 6.5 nV/sqrt Hz, low DC offset voltage of +/- 150 uV maximum at 25 degrees C and low offset voltage temperature coefficient of 1.5 uV/C to improve system sensitivity and accuracy.

The LMP7721 has a supply voltage range of 1.8V to 5.5V and is offered in an 8-pin SOIC package with a special pinout that isolates the amplifier's input from the power supply and output pins. This unique pinout further reduces system errors by preventing printed circuit board (PCB) leakage current from reaching the input pins. By using the LMP7721 in place of an amplifier and discrete dual-input MOSFET, system designers can realize PCB space savings of approximately 50 percent.

SOURCE: National Semiconductor Corp.