AD549JHZ

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1. DESCRIPTION

The AD549JHZ 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. The AD549JHZ is suited for applications requiring very low input current and low input offset voltage. It excels as a preamp for a wide variety of current output transducers, such as photodiodes, photomultiplier tubes, or oxygen sensors. The AD549JHZ can also be used as a precision integrator or low droop sample-and-hold. The AD549JHZ is pin compatible with standard FET and electrometer op amps, allowing designers to upgrade the performance of present systems at little additional cost. The AD549JHZ is available in a TO-99 hermetic package. The case is connected to Pin 8, thus, the metal case can be independently connected to a point at the same potential as the input terminals, minimizing stray leakage to the case. The AD549JHZ is available in four performance grades. The J, K, and L versions are rated over the commercial temperature range of 0°C to +70°C. The S grade is specified over the military temperature range of −55°C to +125°C and is available processed to MIL-STD-883B, Rev. C. Extended reliability plus screening is also available. Plus screening includes 168 hour burn-in, as well as other environmental and physical tests derived from MIL-STD-883B, Rev. C.

2. FEATURES

    1. Ultralow input bias current

        - 60 fA maximum (AD549L)

        - 100 fA maximum (AD549K)

        - 250 fA maximum (AD549J)

    2. Input bias current guaranteed over the common-mode voltage range

    3. Low offset voltage

        - 0.50 mV maximum (AD549K)

        - 1.00 mV maximum (AD549J)

    4. Low offset drift

        - 15 μV/°C maximum (AD549K)

        - 20 μV/°C maximum (AD549J)

    5. Low power

        - 700 μA maximum supply current

        - Low input voltage noise

    6. 4 μV (typ) p-p over 0.1 Hz to 10 Hz

3. PRODUCT HIGHLIGHTS

    1. The AD549 input currents are specified, 100% tested, and guaranteed after the device is warmed up. They are guaranteed over the entire common-mode input voltage range.

    2. The AD549 input offset voltage and drift are laser trimmed to 0.50 mV and 15 μV/°C (AD549K), and to 1 mV and 20 μV/°C (AD549J).

    3. A maximum quiescent supply current of 700 μA minimizes heating effects on input current and offset voltage.

    4. AC specifications include 1 MHz unity-gain bandwidth and 3 V/μs slew rate. Settling time for a 10 V input step is 5 μs to 0.01%. 

4. APPLICATIONS

    1. Electrometer amplifier

    2. Photodiode preamp

    3. pH electrode buffer