AD8638ARZ

Overview

The AD8638ARZ is a single-channel, auto-zero operational amplifier manufactured by Analog Devices Inc. It features rail-to-rail output swing and operates on a single supply from 5 V to 16 V or dual supplies from ±2.5 V to ±8 V. Key electrical specifications include a maximum offset voltage of 9 μV, an offset drift of 0.04 μV/°C (excluding SOT-23), and a maximum input bias current of 40 pA. The device provides a typical large signal voltage gain of 136 dB, a gain bandwidth product of 1.5 MHz, and a slew rate of 2 V/μs at 16 V operation. It consumes a maximum supply current of 1.3 mA per amplifier.

Feature Summary

• Utilizes a patented ping-pong auto-zeroing topology that combines chopping and auto-zeroing techniques to minimize low-frequency noise and digital switching artifacts without requiring external filtering capacitors.
• Delivers ultrahigh precision with extremely low offset voltage and temperature drift, ensuring stable performance across the extended industrial temperature range of −40°C to +125°C.
• Features rail-to-rail output capability that maximizes signal-to-noise ratio by allowing the output voltage to swing close to both power supply rails.

Applications

• Pressure and position sensors
• Strain gage amplifiers
• Medical instrumentation
• Thermocouple amplifiers
• Precision current sensing

Procurement Notes

Verify the package type matches the required PCB footprint, as the AD8638 series includes multiple options such as 5-lead SOT-23 and 8-lead SOIC. Confirm the specific suffix indicates the correct packaging format for assembly processes. Ensure the operating environment stays within the specified voltage and temperature limits to maintain guaranteed accuracy. Cross-reference the datasheet revision to confirm all electrical characteristics align with the design requirements.

Selection Notes

Select this component when high DC precision is critical and low noise is required without the complexity of external filter components. It is suitable for applications where traditional chopper amplifiers introduce unacceptable switching noise. Consider the 8-lead SOIC package for standard surface-mount assembly if space constraints do not necessitate the smaller SOT-23 option. Evaluate the trade-off between the wide bandwidth and the ultra-low offset for optimal system performance.

Part Context

The AD8638ARZ belongs to the AD8638/AD8639 family of wide bandwidth, auto-zero operational amplifiers. This series is designed to provide the benefits of expensive zero-drift amplifiers at a lower cost. While the AD8638 is a single-channel device, the family also includes the dual-channel AD8639. These amplifiers are part of Analog Devices' broader portfolio of precision analog signal chain products.

Replacement Considerations

The AD8639 is the dual-channel equivalent in the same family. Other members of the auto-zero op amp series include the AD8628 and AD8538 for lower voltage applications. Verify pin compatibility and electrical specifications before substituting with other zero-drift amplifiers.

FAQ

Does the AD8638 require external capacitors for its auto-zero function?

No, the AD8638 utilizes an internal patented topology that eliminates the need for external capacitors for auto-zeroing or chopping functions.

What is the input voltage range limitation for the AD8638?

The inputs are not rail-to-rail; they must be maintained within the specified common-mode range, typically staying at least 2 V below the positive supply rail to prevent output phase reversal.

How does the AD8638 handle overload recovery time?

The device is designed to settle internal nulling loops within two clock cycles after saturation, resulting in an overload recovery time of less than 50 μs.