Analog Devices Inc. AD8221BRZ

Overview

AD8221BRZ from Analog Devices is a precision instrumentation amplifier in 8-lead SOIC package, delivering 90 dB minimum CMRR (G = 1), 25 µV max input offset voltage, and 8 nV/√Hz input voltage noise at 1 kHz - optimized for bridge sensor signal conditioning in industrial weigh scales and medical transducer interfaces.

For engineers reviewing the AD8221BRZ datasheet, AD8221BRZ pinout, AD8221BRZ application, or AD8221BRZ equivalent, key selection criteria include gain-setting resistor dependency (G = 1 + 49.4 kΩ/RG), ±2.3 V to ±18 V dual-supply operation, −40°C to +85°C specified performance range, and RTI noise of 0.25 µV p-p (0.1 Hz to 10 Hz, G ≥ 100).

Technical Context

The AD8221BRZ implements a laser-trimmed 3-op-amp topology with superbeta input transistors and integrated IB compensation, enabling high input impedance (100 GΩ || 2 pF differential), low input bias current (0.4 nA max), and stable CMRR up to 10 kHz (80 dB min at G = 1). Its current-feedback architecture ensures gain-bandwidth product increases with gain - 825 kHz at G = 1, 14.7 kHz at G = 1000.

Pinout symmetry (RG pins adjacent to inputs, REF next to VOUT) minimizes layout-induced CMRR degradation. The REF terminal allows precise output level-shifting relative to a low-impedance source, supporting direct interfacing with ±5 V or single-supply ADCs without external level translation.

Key Specifications

Pinout & Package

AD8221BRZ is housed in an 8-lead SOIC package (body width 3.9 mm, JEDEC MS-012), with θJA = 121°C/W on 4-layer board. Pin functions are validated per Analog Devices Rev. C datasheet Figure 3 and Table 5.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar instrumentation amplifier applications.

Compared with AD8221BRZ, AD8421ARMZ offers superior noise and CMRR for demanding measurement systems, while INA128UA provides cost-effective performance for general-purpose industrial sensing - neither matches AD8221BRZ's balance of precision, flexibility, and SOIC footprint.

Availability

AD8221BRZ is available at Aetrix Electronics and suitable for industrial weigh scales, medical transducer interfaces, and precision data acquisition systems requiring stable component supply, long-term lifecycle assurance, and guaranteed traceability.

Supply support for AD8221BRZ includes scheduled delivery planning, volume procurement assistance, BOM continuity management, traceable sourcing, and lifecycle availability coordination for OEM customers, industrial embedded developers, connected-device designers, and electronics production programs.

Manufacturer

Analog Devices is a global leader in high-performance analog, mixed-signal, and digital signal processing semiconductors, headquartered in Norwood, MA, with design centers worldwide and ISO 9001-certified manufacturing.

The AD8221 belongs to Analog Devices' precision instrumentation amplifier product line, engineered specifically for high-accuracy, low-drift signal conditioning of low-level sensor outputs in harsh industrial and medical environments.

FAQ

What is the maximum gain achievable with AD8221BRZ?

The AD8221BRZ supports a gain range of 1 to 1000, set by a single external resistor using the formula G = 1 + (49.4 kΩ / RG). At G = 1000, RG = 49.9 Ω (1% tolerance recommended). The amplifier remains stable and specified across this full range, with bandwidth decreasing predictably from 825 kHz (G = 1) to 14.7 kHz (G = 1000). AD8221BRZ achieves this via its current-feedback architecture, avoiding the bandwidth collapse typical of voltage-feedback instrumentation amplifiers.

Does AD8221BRZ require external capacitors for stability?

No, AD8221BRZ is unity-gain stable and does not require external compensation capacitors. Stability is ensured internally across the full gain range (1 to 1000) and supply conditions (±2.3 V to ±18 V). However, local 0.1 µF ceramic bypass capacitors are mandatory on both +VS and −VS pins, placed within 2 mm of the device, to suppress high-frequency supply noise and prevent oscillation. AD8221BRZ's internal compensation eliminates layout-dependent instability risks common in discrete op-amp in-amp implementations.

Can AD8221BRZ operate from a single supply?

Yes, AD8221BRZ operates on single supplies (e.g., +5 V, +12 V, +24 V) as well as dual supplies. When using single supply, the reference (REF) pin must be biased to a mid-rail voltage (e.g., +2.5 V for +5 V supply) to establish proper output common-mode level. Input common-mode range extends from −VS + 1.9 V to +VS − 1.2 V, allowing direct connection of grounded sensors. AD8221BRZ's rail-to-rail output swing capability (−VS + 1.2 V to +VS − 1.4 V) ensures full dynamic range utilization in single-supply configurations.

How does the REF pin function in AD8221BRZ?

The REF pin defines the output common-mode voltage: VOUT = G × (VIN+ − VIN−) + VREF. It accepts any low-impedance voltage source between −VS and +VS, enabling level-shifting to match downstream ADC input ranges (e.g., 0 V to +5 V or ±2.5 V). Driving REF with a precision voltage reference or DAC output allows programmable offset adjustment without affecting gain accuracy. AD8221BRZ's REF input impedance is 20 kΩ, so source impedance must be <100 Ω to avoid gain error. This feature eliminates external summing amplifiers in most signal chain architectures.

What is the operating temperature range for AD8221BRZ?

AD8221BRZ is specified for full performance over the industrial temperature range of −40°C to +85°C, with parameters including CMRR, offset voltage, and noise guaranteed across this span. It remains operational up to +125°C, though certain parameters (e.g., offset drift, CMRR) degrade beyond +85°C and are not tested or guaranteed. The BR grade designation confirms compliance with these extended-range specifications. AD8221BRZ's thermal characteristics (θJA = 121°C/W) support reliable operation in enclosed industrial enclosures without forced air cooling.