Part A
AD8421BRZ
テキサス・インスツルメンツ
- Lifecycle
- Active
- Stock
- 1263 個数
- Package
- SOIC-8
- Series
- リニアアンプ - 計装用、オペアンプ、バッファアンプ
Replacement verdict
Compatible functional replacement candidate
The AD8429ARZ and AD8421BRZ are both precision instrumentation amplifiers from Analog Devices in the same SOIC-8 package, sharing a functionally equivalent pinout and gain-setting architecture. While the AD8421BRZ offers a higher bandwidth-to-gain ratio and lower input voltage noise, the AD8429ARZ provides lower input bias current and comparable DC precision, making it a viable functional substitute in most low-frequency, high-impedance signal-conditioning applications. Designers should validate noise, bandwidth, and gain accuracy requirements against the target circuit before finalizing the replacement.
Package and Pinout
High match
Gain Configuration
High match
Input Voltage Noise
Validation required
Bandwidth and Slew Rate
Validation required
Key differences
Rows are prioritized by design impact. Highlighted values require attention during substitution.
Key electrical and mechanical differences between the two devices
| Parameter | AD8429ARZ | AD8421BRZ | Why it matters |
|---|---|---|---|
| Input Voltage Noise (1 kHz, typ) | 1 nV/√Hz | 3 nV/√Hz | Lower input voltage noise improves signal-to-noise ratio for low-level sensor signals, making the AD8429ARZ preferable for very low-noise applications. |
| Gain Bandwidth Product (G = 1, typ) | 15 MHz | 10 MHz | Higher bandwidth supports wider signal frequency ranges and faster settling, which matters for dynamic or high-frequency measurement systems. |
| Input Offset Voltage (max, RTI) | 50 µV | 60 µV | Lower offset voltage reduces DC error at the output, improving accuracy in precision instrumentation and bridge measurement circuits. |
| Input Bias Current (typ) | 100 nA | 1 nA | Much lower bias current in the AD8421BRZ reduces errors with high-impedance sources, making it better suited for sensors with large source impedance. |
| CMRR (G = 100, min) | 110 dB | 114 dB | Higher common-mode rejection suppresses interference and noise from the common-mode voltage, critical for extracting small differential signals in noisy environments. |
| Supply Voltage Range | ±4 V to ±18 V | ±2.5 V to ±18 V | A wider low-end supply range allows the AD8421BRZ to operate on lower supply rails, enabling use in low-power or battery-powered systems. |
| Quiescent Supply Current (typ) | 4.5 mA | 2.3 mA | Lower quiescent current reduces power consumption, which is important for portable and power-sensitive instrumentation designs. |
| Operating Temperature Range | -40°C to +125°C | -40°C to +85°C | A wider high-temperature range makes the AD8429ARZ suitable for harsh industrial and automotive environments requiring extended temperature operation. |
| Package | 8-Lead SOIC | 8-Lead SOIC | Identical package and pinout allow direct board-level substitution without layout changes. |
Need help validating a replacement?
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Full specification comparison
Use manufacturer datasheets as the final authority.
| Specification | AD8421BRZ | AD8429ARZ |
|---|---|---|
| Part Status | Active | Active |
| Amplifier Type | Instrumentation | Instrumentation |
| Number of Circuits | 1 | 1 |
| Slew Rate | 35V/µs | 22V/µs |
| -3 dB Bandwidth | 10 MHz | 15 MHz |
| Current - Input Bias | 100 pA | 300 nA |
| Voltage - Input Offset | 25 µV | 150 µV |
| Supply Current | 2mA | 6.7mA |
| Current - Output / Channel | 65 mA | 35 mA |
| Voltage - Supply Span(Min) | 5 V | 8 V |
| Voltage - Supply Span(Max) | 36 V | 36 V |
| Operating Temperature | -40°C ~ 85°C | -40°C ~ 125°C |
| Mounting Type | Surface Mount | Surface Mount |
Frequently asked questions
What are the key differences between the AD8429ARZ and AD8421BRZ instrumentation amplifiers?
The AD8429ARZ is a low-noise instrumentation amplifier with a gain range of 1 to 10,000, a typical input voltage noise of 1 nV/√Hz at 1 kHz, and a typical gain bandwidth product of 15 MHz at G = 100. The AD8421BRZ is a lower-power instrumentation amplifier with a typical input voltage noise of 3 nV/√Hz at 1 kHz, a typical gain bandwidth product of 10 MHz at G = 100, and a lower typical supply current of 2.3 mA versus 4.5 mA for the AD8429. Both are specified for operation on ±5 V to ±18 V dual supplies and are offered in 8-lead SOIC packages.
Are the AD8429ARZ and AD8421BRZ pin-compatible?
Yes. Both devices are offered in an 8-lead SOIC package with the same pinout: -IN, +IN, -VS, +VS, REF, OUT, and two gain-setting resistor pins (RG). This allows the AD8421BRZ to be evaluated as a potential replacement for the AD8429ARZ on the same PCB footprint, provided the electrical differences are validated for the target design.
Which device offers lower input voltage noise?
The AD8429ARZ offers lower input voltage noise, with a typical value of 1 nV/√Hz at 1 kHz, compared with a typical value of 3 nV/√Hz at 1 kHz for the AD8421BRZ. The AD8429 is therefore better suited to low-level signal applications where input-referred noise is a dominant design constraint.
Which device consumes less supply current?
The AD8421BRZ consumes less supply current, with a typical value of 2.3 mA, compared with a typical value of 4.5 mA for the AD8429ARZ. The AD8421 is therefore preferable in power-sensitive designs where the lower quiescent current is beneficial.
What is the gain bandwidth product of each device?
The AD8429ARZ has a typical gain bandwidth product of 15 MHz at G = 100, while the AD8421BRZ has a typical gain bandwidth product of 10 MHz at G = 100. The AD8429 therefore provides wider closed-loop bandwidth at a given gain, which can be advantageous for higher-frequency signal conditioning.
What supply voltage range do both devices support?
Both the AD8429ARZ and AD8421BRZ are specified for operation on dual supplies from ±5 V to ±18 V. Designs should confirm the specific supply range and associated specifications in the respective manufacturer datasheets for the intended operating conditions.
Can the AD8421BRZ be used as a drop-in replacement for the AD8429ARZ?
Because both devices share the same 8-lead SOIC pinout and support the same ±5 V to ±18 V supply range, the AD8421BRZ can be considered for the same footprint. However, it is not a direct drop-in replacement without validation: the AD8421BRZ has higher input voltage noise (3 nV/√Hz vs 1 nV/√Hz typical at 1 kHz), lower gain bandwidth product (10 MHz vs 15 MHz typical at G = 100), and lower supply current (2.3 mA vs 4.5 mA typical). These differences must be evaluated against the target design requirements.
Which device is better suited for low-power designs?
The AD8421BRZ is better suited for low-power designs because its typical supply current of 2.3 mA is lower than the 4.5 mA typical supply current of the AD8429ARZ. The trade-off is higher input voltage noise and lower gain bandwidth product compared with the AD8429ARZ.