Features and Benefits
- Ultralow input bias current
- 60 fA maximum (AD549L)
- 100 fA maximum (AD549K)
- 250 fA maximum (AD549J)
- Input bias current guaranteed over the common-mode voltage range
- Low offset voltage
- 0.50 mV maximum (AD549K)
- 1.00 mV maximum (AD549J)
- Low offset drift
- 15 µV/°C maximum (AD549K)
- 20 µV/°C maximum (AD549J)
- Low power
- 700 µA maximum supply current
- Low input voltage noise
- 4 µV (typ) p-p over 0.1 Hz to 10 Hz
- MIL-STD-883B parts available
The AD549 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 common-mode voltage.
The AD549 is suited for applications that require very low input current and low input offset voltage. It excels as a preamp for a wide variety of current output transducers, such as photo-diodes, photomultiplier tubes, or oxygen sensors. The AD549 can also be used as a precision integrator or low droop sample and hold. The AD549 is pin compatible with standard FET and electrometer op amps, allowing designers to upgrade the performance of present systems at little additional cost.
The AD549 is available in a TO-99 hermetic package. The case is connected to Pin 8 so that 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 AD549 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.
- 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.
- 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)..
- A maximum quiescent supply current of 700 μA minimizes heating effects on input current and offset voltage.
- 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%.
- Electrometer amplifier
- Photodiode preamp
- pH electrode buffer
Markets and Technologies
Product Lifecycle Production
At least one model within this product family is in production and available for purchase. The product is appropriate for new designs but newer alternatives may exist.
Tools & Simulations
LTspice® is a powerful, fast and free simulation software, schematic capture and waveform viewer with enhancements and models for improving the simulation of analog circuits.
Models for the following parts are available in LTspice:
Use the Analog Filter Wizard to design low-pass, high-pass, or band-pass filters with actual op amps in minutes. As you progress through the design process, you can observe the characteristics of your filter design from ideal specifications to real world circuit behavior. Quickly evaluate the tradeoffs in op amp specifications - including gain-bandwidth, noise, and supply current – to determine the best filter design for your requirements.
Use Photodiode Wizard to design a transimpedance amplifier circuit to interface with a photodiode. Select a photodiode from the library included in the tool, or enter custom photodiode specifications. Quickly observe tradeoffs between Bandwidth, Peaking (Q), and ENOB/SNR. Modify circuit parameters, and immediately see results in plots for pulse response, frequency response, and noise gain.
ADI has always placed the highest emphasis on delivering products that meet the maximum levels of quality and reliability. We achieve this by incorporating quality and reliability checks in every scope of product and process design, and in the manufacturing process as well. "Zero defects" for shipped products is always our goal.
Sample & Buy
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