AD8421BRZ - 3nV/√Hz Low Power Instr Amp | Analog Devices
MPN: AD8421BRZ ✓ Active| Qty | Unit Price | Extended |
|---|---|---|
| 1 | $8.12 | $8.12 |
| 10 | $7.32 | $73.20 |
| 100 | $6.36 | $636.00 |
| 500 | $5.8 | $2,900.00 |
| 1,000 | $5.35 | $5,350.00 |
| 3,000 | $4.9 | $14,700.00 |
Drop-in alternatives for AD8421BRZ — same package, pin-to-pin compatible. Different-package parts requiring PCB rework are excluded.
Quick Comparison Tool — Select alternative parts for side-by-side comparison:
AD8421ARZ
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View Datasheet →AD8221ARZ
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View Datasheet →AD8223ARZ
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View Datasheet →INA128UA
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AD8421BRZ Maximum Ratings & Electrical Characteristics
| Amplifier Type | Instrumentation Amplifier |
| Number of Circuits | 1 |
| Voltage Noise Density | 3 nV/√Hz typ |
| Bandwidth | 10 MHz (G=1) |
| Supply Voltage - Single | 5 V to 36 V |
| Supply Voltage - Dual | ±2.5 V to ±18 V |
| Quiescent Current | 2.3 mA typ |
| Input Bias Current | 250 pA max |
| Input Offset Voltage | 60 µV max (B grade) |
| CMRR | 126 dB min (G=100) |
| Gain Range | 1 to 10000 |
| Gain Drift | [DATA_NEEDED: gain drift] |
| Operating Temperature | -40°C to +85°C |
| Package | 8-Lead SOIC |
| Mounting Type | Surface Mount |
| RoHS Status | Compliant |
| REACH Status | Compliant |
AD8421BRZ Pin Configuration
| Pin 1 | RG- — Gain setting resistor negative terminal |
| Pin 2 | -IN — Inverting differential input |
| Pin 3 | +IN — Non-inverting differential input |
| Pin 4 | -VS — Negative supply or ground for single-supply operation |
| Pin 5 | REF — Reference voltage pin for output offset |
| Pin 6 | OUT — Instrumentation amplifier output |
| Pin 7 | +VS — Positive supply |
| Pin 8 | RG+ — Gain setting resistor positive terminal |
Safe Operating Area (SOA) & Thermal Characteristics
No official SOA curve available for this component. Always operate within absolute maximum ratings specified in the datasheet. Ensure adequate cooling and derate as needed.
Typical Applications
AD8421BRZ is suitable for 6 applications: Medical ECG and Patient Monitoring, High-Speed Data Acquisition Systems, Industrial Process Control and Bridge Sensing, Precision Sensor Signal Conditioning, Motor Control Current Sensing, Test and Measurement Instrumentation.
Medical ECG and Patient Monitoring
The AD8421BRZ is ideal for ECG front ends because its 3 nV/√Hz voltage noise and 126 dB CMRR preserve weak biopotential signals in the presence of 50/60 Hz interference. Its ultralow 250 pA input bias current minimizes errors from high-impedance electrodes, and the 2.3 mA quiescent current supports portable monitors. Differential signal amplification into a high-resolution ADC such as the AD7175-2BRUZ or AD7988-5BCPZ provides excellent system accuracy.
Recommended
High-Speed Data Acquisition Systems
With a 10 MHz bandwidth at G=1, the AD8421BRZ is suited for high-speed DAQ systems that must capture fast transients and dynamic sensor signals. The low noise density supports high dynamic range, while the reference pin allows easy offset adjustment for unipolar ADC interfaces. In a typical channel, the AD8421BRZ output is connected to a SAR ADC such as the AD7988-5BCPZ or AD7172-2BRUZ, enabling simultaneous high-speed and high-precision measurement.
Recommended
Industrial Process Control and Bridge Sensing
The AD8421BRZ can interface directly with strain-gauge bridges and pressure sensors in industrial automation. Its high CMRR rejects common-mode noise from long cable runs, while the low offset drift minimizes measurement error over temperature. The wide supply range of ±2.5 V to ±18 V or 5 V to 36 V simplifies powering from industrial 24 V rails. The output can drive an external ADC or a precision comparator for control-loop monitoring.
Recommended
Precision Sensor Signal Conditioning
The AD8421BRZ provides the low noise and high input impedance needed for a wide variety of sensors, including thermocouples, RTDs, and photodetectors. Its ultralow input bias current minimizes loading on high-impedance sources, while the 10 MHz gain-bandwidth product supports real-time processing. Used together with precision amplifiers such as the ADA4522-2ARZ, the signal chain can achieve very low offset and drift suitable for laboratory-grade instrumentation.
Recommended
Motor Control Current Sensing
The AD8421BRZ can be used in motor control applications to amplify the small differential voltage across a current-sense resistor. Its high bandwidth of 10 MHz at G=1 supports fast current-control loops, while the low noise and high CMRR reject motor-drive switching noise. The wide common-mode input range and supply flexibility allow direct connection to shunt resistors in both low-side and high-side current-sense configurations.
Recommended
Test and Measurement Instrumentation
For bench instruments, low noise and high CMRR are essential to make accurate voltage and sensor measurements. The AD8421BRZ offers a compact 8-lead SOIC solution with 3 nV/√Hz noise, 10 MHz bandwidth, and a reference pin for output offset trimming. It can be used as the analog front end for multimeters, thermocouple meters, or precision source-measure units, feeding digitizers such as the AD7606BSTZ-4RL or AD7172-2BRUZ.
Recommended
Recommended Products Summary
Engineering reference data for AD8421BRZ — comparison, design guidance, and compliance information.
Selection Guide
Comparison with Alternatives
| Parameter | This Product | AD8421ARZ | AD8221ARZ | INA128UA |
|---|---|---|---|---|
| Package | 8-SOIC | 8-SOIC | 8-SOIC | 8-SOIC |
| Brand | Analog Devices | Analog Devices | Analog Devices | Texas Instruments |
| Voltage Noise Density | 3 nV/√Hz | 3 nV/√Hz | 8 nV/√Hz | 8 nV/√Hz |
| Bandwidth at G=1 | 10 MHz | 10 MHz | 1 MHz | 1.3 MHz |
| Supply Voltage Range | ±2.5 V to ±18 V or 5 V to 36 V | ±2.5 V to ±18 V or 5 V to 36 V | ±2.5 V to ±18 V or 5 V to 36 V | ±2.25 V to ±18 V or 4.5 V to 36 V |
| Input Bias Current | 250 pA max | 250 pA max | 250 pA max | 5 nA max |
| CMRR at G=100 | 126 dB min | 126 dB min | 120 dB min | 120 dB min |
| Quiescent Current | 2.3 mA | 2.3 mA | 0.9 mA | 0.7 mA |
| Grade | B grade, industrial temperature | A grade, industrial temperature | Precision grade, industrial temperature | Standard grade, industrial temperature |
Key Differentiators
- Lowest voltage noise in the AD8421/AD8221 comparison (vs AD8221ARZ)
- 10 MHz unity-gain bandwidth supports high-speed DAQ (vs INA128UA)
- Ultralow input bias current preserves sensor accuracy (vs AD620ARZ)
- Grade selection for precision systems (vs AD8421ARZ)
Design Notes
Place the gain-setting resistor (RG) directly between pins 1 and 8 to minimize parasitic inductance and capacitance. Stray capacitance at these pins can reduce bandwidth and cause gain peaking. Use a precision metal-film resistor with 0.1% tolerance or better when the gain accuracy is critical. For high-gain configurations, keep traces short and the resistor body close to the IC body.
Filter the reference pin with a low-impedance source. The reference pin (pin 5) sets the output common-mode voltage and must be driven from a low-impedance reference or buffer. For single-supply circuits, set the reference to mid-supply to maximize output swing. If using an external reference, place a 0.1 µF and 1 µF capacitor directly at the pin for noise bypass.
Do not exceed the input common-mode voltage range. Although the AD8421 has excellent CMRR, exceeding the specified input voltage range will degrade linearity and can damage the device. Add series protection resistors and clamp diodes for harsh industrial environments. Also ensure the power supply is clean and decoupled with 0.1 µF ceramic capacitors close to each supply pin.
Compliance Information
Compliance values based on distributor and product page data for AD8421BRZ. AEC-Q100 not applicable for this standard instrumentation amplifier.
