Part A
AD8642ARZ
Analog Devices Inc.
- Lifecycle
- Active
- Stock
- 5899 PCS
- Package
- SOIC-8
- Series
- Linear - Amplifiers - Instrumentation, OP Amps, Buffer Amps
Replacement verdict
Compatible functional replacement candidate
The AD8646ARZ and AD8642ARZ are both dual low-power JFET-input operational amplifiers in the same SOIC-8 package with identical pinout, making the AD8646ARZ a viable functional replacement candidate for the AD8642ARZ in most designs. However, the AD8646ARZ offers a higher gain-bandwidth product and faster slew rate, so supply decoupling, stability, and capacitive-load behavior should be validated in the target circuit before committing to production.
Amplifier Channel Count
High match
Package and Pinout
High match
Supply Voltage Range
High match
Gain-Bandwidth Product
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 | AD8646ARZ | AD8642ARZ | Why it matters |
|---|---|---|---|
| Number of Amplifiers | 2 | 2 | Both are dual op-amps, so channel count is identical and does not affect substitutability. |
| Input Offset Voltage (max) | 2.5 mV | 0.75 mV | Lower offset voltage improves DC precision; the AD8642 offers tighter offset, which matters for precision signal chains. |
| Input Bias Current (typ) | 0.3 pA | 0.3 pA | Ultra-low CMOS input bias current is critical for high-impedance sensor and photodiode applications; both are equivalent here. |
| Gain Bandwidth Product | 24 MHz | 3.5 MHz | GBW determines the maximum signal frequency for a given gain; the AD8646 supports much wider bandwidth applications. |
| Slew Rate | 11 V/µs | 3 V/µs | Higher slew rate enables faster large-signal response; the AD8646 is better suited for higher-speed dynamic signals. |
| Supply Voltage Range | 2.7 V to 5.5 V | 5 V to 26 V | Operating supply range dictates compatibility with the system rail; the AD8646 is single-supply low-voltage, while the AD8642 supports higher-voltage rails. |
| Supply Current per Amplifier (typ) | 1.4 mA | 0.8 mA | Quiescent current affects power budget; the AD8642 draws less current per amplifier, benefiting low-power designs. |
| Input Voltage Noise Density (1 kHz) | 8 nV/√Hz | 16 nV/√Hz | Lower noise density improves SNR in low-level signal amplification; the AD8646 provides better noise performance. |
| Package | 8-Lead SOIC | 8-Lead SOIC | Identical package and pinout allow drop-in board compatibility without layout changes. |
Need help validating a replacement?
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Full specification comparison
Use manufacturer datasheets as the final authority.
| Specification | AD8642ARZ | AD8646ARZ |
|---|---|---|
| Part Status | Active | Active |
| Amplifier Type | J-FET | General Purpose |
| Number of Circuits | 2 | 2 |
| Output Type | Rail-to-Rail | Rail-to-Rail |
| Slew Rate | 3V/µs | 11V/µs |
| Gain Bandwidth Product | 3.5 MHz | 24 MHz |
| Current - Input Bias | 0.25 pA | 0.3 pA |
| Voltage - Input Offset | 70 µV | 600 µV |
| Supply Current | 200µA (x2 Channels) | 1.5mA (x2 Channels) |
| Current - Output / Channel | 12 mA | 120 mA |
| Voltage - Supply Span(Min) | 5 V | 2.7 V |
| Voltage - Supply Span(Max) | 26 V | 5.5 V |
| Operating Temperature | -40°C ~ 125°C | -40°C ~ 125°C |
| Mounting Type | Surface Mount | Surface Mount |
Frequently asked questions
What are the primary differences between the AD8646ARZ and AD8642ARZ?
The AD8646ARZ is a dual, low-power, rail-to-rail input/output operational amplifier specified for operation from 2.7 V to 5.5 V, while the AD8642ARZ is a dual, low-noise, precision JFET-input operational amplifier specified for operation from 5 V to 26 V (or ±2.5 V to ±13 V). The AD8646ARZ targets low-voltage, low-power applications with 6.5 MHz gain bandwidth, whereas the AD8642ARZ targets higher-voltage precision applications with 3.5 MHz gain bandwidth and lower input bias current.
Are the AD8646ARZ and AD8642ARZ pin-compatible in the same package?
Both devices are offered in an 8-lead SOIC package (the "RZ" suffix denotes RoHS-compliant SOIC), and both use the standard dual op-amp pinout: pin 1 = OUT A, pin 2 = −IN A, pin 3 = +IN A, pin 4 = V−, pin 5 = +IN B, pin 6 = −IN B, pin 7 = OUT B, pin 8 = V+. However, pin compatibility does not guarantee electrical interchangeability; supply voltage range, input bias current, and dynamic performance differ significantly.
Can the AD8646ARZ and AD8642ARZ be used interchangeably in an existing design?
No, they should not be treated as drop-in replacements without validation. The AD8646ARZ operates from 2.7 V to 5.5 V, while the AD8642ARZ requires a minimum supply of 5 V and supports up to 26 V. A design operating below 5 V cannot use the AD8642ARZ, and a design operating above 5.5 V cannot use the AD8646ARZ. Input bias current, noise, and bandwidth also differ, so circuit performance must be re-verified.
How do the supply voltage ranges of the AD8646ARZ and AD8642ARZ compare?
The AD8646ARZ is specified for single-supply operation from 2.7 V to 5.5 V. The AD8642ARZ is specified for operation from 5 V to 26 V single supply, or ±2.5 V to ±13 V dual supply. The AD8642ARZ therefore supports higher-voltage systems that the AD8646ARZ cannot, while the AD8646ARZ supports lower-voltage systems below the AD8642ARZ minimum.
How do the input bias current and input offset characteristics differ?
The AD8642ARZ is a JFET-input amplifier with very low input bias current (typically in the low picoampere range) and low input offset voltage, making it suitable for high-impedance precision sensing. The AD8646ARZ is a CMOS-input amplifier with input bias current typically in the low picoampere range as well, but its offset voltage and drift specifications differ from the AD8642ARZ. Designers should consult the respective datasheets for the exact guaranteed limits over temperature.
Which device is better suited for low-power portable applications?
The AD8646ARZ is generally the better fit for low-voltage portable applications because it operates down to 2.7 V and is specified with low supply current per amplifier, allowing direct operation from single-cell lithium or 3 V battery rails. The AD8642ARZ requires at least 5 V and is intended for higher-voltage precision signal chains rather than low-voltage battery-powered designs.
How do the gain bandwidth and slew rate of the two amplifiers compare?
The AD8646ARZ provides approximately 6.5 MHz gain bandwidth product with a slew rate around 5 V/µs, while the AD8642ARZ provides approximately 3.5 MHz gain bandwidth product with a slew rate around 3 V/µs. The AD8646ARZ therefore offers wider small-signal bandwidth, whereas the AD8642ARZ emphasizes precision and low noise at higher supply voltages.
What are the typical noise characteristics of the AD8646ARZ and AD8642ARZ?
The AD8642ARZ is specified as a low-noise JFET-input amplifier with typical input voltage noise density in the range of approximately 8 nV/√Hz to 10 nV/√Hz at 1 kHz. The AD8646ARZ has a higher typical input voltage noise density, in the range of approximately 15 nV/√Hz to 20 nV/√Hz at 1 kHz. For low-noise precision signal conditioning, the AD8642ARZ is generally preferred.
Are both the AD8646ARZ and AD8642ARZ RoHS compliant and available in the same package options?
Yes. The "RZ" suffix in both part numbers indicates RoHS-compliant, 8-lead SOIC packaging from Analog Devices. Both are dual operational amplifiers offered in the standard 8-lead SOIC_N package, so board footprint and land pattern are identical, though electrical specifications and supply requirements differ as noted above.