GENERAL DESCRIPTION

The AD5491 is a monolithic electrometer operational amplifier with very low input bias current. Input offset voltage and input offset voltage drift are laser trimmed for precision performance. The ultralow input current of the part is achieved with Topgate? JFET technology, a process development exclusive to Analog Devices, Inc. This technology allows fabrication of extremely low input current JFETs compatible with a standard junction isolated bipolar process. The 1015 Ω common-mode impedance, which results from the bootstrapped input stage, ensures that the input current is essentially independent of the commonmode voltage.

FEATURES

Ultralow input bias current 60 fA maximum (AD549L) 250 fA maximum (AD549J)

Input bias current guaranteed over the common-mode voltage range

Low offset voltage 0.25 mV maximum (AD549K) 1.00 mV maximum (AD549J)

Low offset drift 5 μV/°C maximum (AD549K) 20 μV/°C maximum (AD549J)

Low power 700 μA maximum supply current Low input voltage noise

4 μV p-p over 0.1 Hz to 10 Hz

MIL-STD-883B parts available

APPLICATIONS

Electrometer amplifier

Photodiode preamp

pH electrode buffer

Vacuum ion gauge measurement