Precision amps deliver maximum accuracy with low input bias current

Santa Clara, Calif. — National Semiconductor Corp. has introduced the LMP7721, a precision amplifier with the industry's lowest guaranteed input bias current of 20 fA at room temperature and over the extended temperature range of -40°C to 125° C, according to the company. As a result, the device is said to deliver 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. 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°C, which is 50 percent less than the closest competitive device, said National.

The LMP7721 precision amplifier provides 3 fA, with a guaranteed limit of 20 fA at 25°C, 900 fA at 85°C and 5 pA at 125°C. The amplifier also maintains ultra-low input bias current over its entire input common-mode voltage range, and its wide GBW along with a high open-loop gain of 120 dB enables accurate signal conditioning. Other features include low input voltage noise of 6.5 nV/sqrt Hz, low DC offset voltage of +/- 50 uV maximum at 25°C and low offset voltage temperature coefficient of 1.5 uV/C to improve system sensitivity and accuracy.

The LMP7721 provides a supply voltage range of 1.8 V to 5.5 V 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 is said to further reduce 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, said National.

Pricing: The LMP7721 is available now and priced at $4.95 each in quantities of 1,000.
Product information: LMP7721, Amplifiers Made SimpleSM WEBENCH online design tool, designing with amplifiers, and PowerWise products

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