Part A
AD8421BRZ
Analog Devices Inc.
- Lifecycle
- Active
- Stock
- 1263 PCS
- Package
- SOIC-8
- Series
- Linear - Amplificadores - Instrumentação, OP Amps, Buffer Amps
Replacement verdict
Compatible functional replacement candidate
The AD8422BRZ and AD8421BRZ are both precision instrumentation amplifiers in the same SOIC-8 package with identical pinout, making them strong functional replacement candidates. The AD8422BRZ offers lower supply current and wider supply range, while the AD8421BRZ provides higher bandwidth and faster settling. Designers should validate noise, bandwidth, and gain-bandwidth requirements against the target application before substituting.
Package and Pinout
High match
Supply Voltage Range
High match
Bandwidth and Slew Rate
Validation required
Input Noise Density
Validation required
Parts at a glance
Part B
AD8422BRZ
Analog Devices Inc.
- Lifecycle
- Active
- Stock
- 3871 PCS
- Package
- SOIC-8
- Series
- Linear - Amplificadores - Instrumentação, OP Amps, Buffer Amps
Key differences
Rows are prioritized by design impact. Highlighted values require attention during substitution.
Key electrical and mechanical differences between the two devices
| Parameter | AD8422BRZ | AD8421BRZ | Why it matters |
|---|---|---|---|
| Gain Bandwidth Product (GBP) | 1 MHz | 10 MHz | Determines the maximum frequency at which the amplifier can provide useful gain; the AD8421 supports much higher bandwidth signal chains. |
| Input Voltage Noise (1 kHz) | 8 nV/√Hz | 3 nV/√Hz | Lower input voltage noise improves signal-to-noise ratio for low-level sensor signals; the AD8421 is significantly quieter. |
| Input Offset Voltage (max) | 70 µV | 60 µV | Offset voltage directly adds DC error to the measured signal; a lower maximum offset reduces calibration burden in precision applications. |
| Supply Current per Amplifier | 300 µA | 2.3 mA | Quiescent current affects power budget; the AD8422 is far more suitable for low-power or battery-operated designs. |
| CMRR (DC to 60 Hz, G=1000) | 120 dB | 134 dB | Higher common-mode rejection suppresses interference and ground noise; the AD8421 offers superior rejection for noisy environments. |
| Slew Rate | 0.8 V/µs | 35 V/µs | Slew rate limits large-signal response speed; the AD8421 handles fast transients and higher-frequency signals much better. |
| Supply Voltage Range | 4.6 V to 36 V (±2.3 V to ±18 V) | 5 V to 36 V (±2.5 V to ±18 V) | Defines the allowable power supply; the AD8422 can operate at a slightly lower minimum supply, useful for low-voltage rails. |
| Input Bias Current (max) | 1 nA | 2 nA | Bias current creates offset errors with high source impedances; lower bias current benefits high-impedance sensor interfaces. |
| Operating Temperature Range | -40 °C to +85 °C | -40 °C to +125 °C | Determines suitability for harsh environments; the AD8421 supports higher ambient temperatures for industrial applications. |
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Full specification comparison
Use manufacturer datasheets as the final authority.
| Specification | AD8421BRZ | AD8422BRZ |
|---|---|---|
| Part Status | Active | Active |
| Amplifier Type | Instrumentation | Instrumentation |
| Number of Circuits | 1 | 1 |
| Slew Rate | 35V/µs | 0.8V/µs |
| -3 dB Bandwidth | 10 MHz | 2.2 MHz |
| Current - Input Bias | 100 pA | 200 pA |
| Voltage - Input Offset | 25 µV | 25 µV |
| Supply Current | 2mA | 300µA |
| Current - Output / Channel | 65 mA | 20 mA |
| Voltage - Supply Span(Min) | 5 V | 4.6 V |
| Voltage - Supply Span(Max) | 36 V | 36 V |
| Operating Temperature | -40°C ~ 85°C | -40°C ~ 85°C |
| Mounting Type | Surface Mount | Surface Mount |
| Output Type | - | Rail-to-Rail |
Frequently asked questions
What are the key differences between the AD8422BRZ and AD8421BRZ instrumentation amplifiers?
Both are precision instrumentation amplifiers in an 8-lead SOIC package, but they differ in supply range, bandwidth, and noise. The AD8422BRZ operates on ±2.3 V to ±18 V (or 4.6 V to 36 V single supply) with 2.2 MHz bandwidth and 8 nV/√Hz input voltage noise. The AD8421BRZ operates on ±2.5 V to ±18 V (or 5 V to 36 V single supply) with 10 MHz bandwidth and 3 nV/√Hz input voltage noise. The AD8421BRZ is faster and lower noise, while the AD8422BRZ offers a wider low-supply margin and lower power consumption.
Are the AD8422BRZ and AD8421BRZ pin-compatible?
Yes. Both devices are offered in the same 8-lead SOIC package with identical pin functions (gain resistor pins, +IN, -IN, REF, OUTPUT, +VS, -VS), so they are pin-compatible and share the same PCB land pattern.
Can the AD8422BRZ and AD8421BRZ be used as direct substitutes for each other?
They are pin-compatible but not electrically identical. Substitution requires verifying supply voltage, gain setting, bandwidth, noise, and power dissipation against the target design. The AD8421BRZ requires a minimum 5 V single supply (or ±2.5 V), whereas the AD8422BRZ can operate down to 4.6 V single supply (or ±2.3 V), so the AD8422BRZ can replace the AD8421BRZ in lower-supply designs, but not necessarily the reverse.
How do the gain-setting configurations compare between the AD8422BRZ and AD8421BRZ?
Both use a single external resistor between the RG pins to set gain, with the gain equation G = 1 + (19.8 kΩ / RG) for the AD8422BRZ and G = 1 + (9.9 kΩ / RG) for the AD8421BRZ. Because the internal gain resistors differ, the same RG value produces different gains on the two devices, so the gain resistor must be recalculated when substituting.
Which device offers lower input voltage noise, the AD8422BRZ or the AD8421BRZ?
The AD8421BRZ has lower input voltage noise at 3 nV/√Hz (typical, at 1 kHz), compared with 8 nV/√Hz (typical, at 1 kHz) for the AD8422BRZ. The AD8421BRZ is therefore preferable for low-noise signal acquisition, while the AD8422BRZ trades higher noise for lower supply current.
How do the bandwidth and supply current of the AD8422BRZ and AD8421BRZ compare?
The AD8421BRZ provides 10 MHz bandwidth (G = 1) and typically draws 2.3 mA supply current. The AD8422BRZ provides 2.2 MHz bandwidth (G = 1) and typically draws 300 µA supply current. The AD8421BRZ suits higher-frequency signals, while the AD8422BRZ suits low-power, lower-bandwidth applications.
What are the operating temperature ranges for the AD8422BRZ and AD8421BRZ?
Both the AD8422BRZ and AD8421BRZ are specified over the industrial temperature range of −40 °C to +85 °C, as stated in their respective manufacturer datasheets.
Do the AD8422BRZ and AD8421BRZ share the same CMRR and input offset specifications?
No. The AD8422BRZ specifies CMRR of 94 dB minimum (G = 1) and input offset voltage of 70 µV maximum (B grade). The AD8421BRZ specifies CMRR of 80 dB minimum (G = 1) and input offset voltage of 60 µV maximum (B grade). Designers should confirm the exact grade-specific limits in the respective datasheets before substitution.