Part A
AD847AR
Analog Devices Inc.
- Lifecycle
- Active
- Stock
- 7655 PCS
- Series
- Linear - Amplifiers - Instrumentation, Op Amps, Buffer Amps
Replacement verdict
Not a drop-in replacement
The AD8479BRZ and AD847AR are not functionally interchangeable. The AD8479BRZ is a precision high common-mode voltage difference amplifier, while the AD847AR is a high-speed operational amplifier; they differ in amplifier topology, input architecture, and package footprint, so the AD847AR cannot serve as a direct substitute in AD8479BRZ applications.
Different amplifier topology
Different input architecture
Different package footprint
Different bandwidth class
Key differences
Rows are prioritized by design impact. Highlighted values require attention during substitution.
Key electrical and mechanical differences between the two devices
| Parameter | AD8479BRZ | AD847AR | Why it matters |
|---|---|---|---|
| Amplifier Type | Difference Amplifier | High Speed Operational Amplifier | These are fundamentally different functional blocks; a difference amplifier extracts a differential signal, while a high-speed op amp is a general-purpose building block, so they are not directly substitutable. |
| Number of Channels | 1 | 1 | Both are single-channel devices, so channel count does not differentiate them for substitution purposes. |
| Gain Bandwidth Product | 0.13 MHz | 50 MHz | The AD847AR offers far greater bandwidth, making it suitable for high-speed signal processing, whereas the AD8479BRZ is limited to low-frequency precision applications. |
| Slew Rate | 0.5 V/µs | 300 V/µs | Slew rate determines how fast the output can respond to input changes; the AD847AR is dramatically faster, which is critical for large-signal high-frequency applications. |
| Input Offset Voltage | ±0.5 mV (max) | ±5 mV (max) | Lower offset voltage improves DC accuracy; the AD8479BRZ provides better precision for low-level signal measurement. |
| Supply Voltage Range | ±4 V to ±18 V (dual) | ±4.5 V to ±18 V (dual) | The slightly wider low-end supply range of the AD8479BRZ allows operation at lower supply voltages, affecting compatibility in low-voltage systems. |
| Input Common-Mode Voltage Range | ±600 V | Limited to supply rails | The AD8479BRZ is designed for high common-mode voltage sensing, while the AD847AR cannot tolerate voltages beyond its supply rails, making them unsuitable as substitutes in high-voltage sensing applications. |
| Operating Temperature Range | -40 °C to +125 °C | -40 °C to +85 °C | The wider temperature range of the AD8479BRZ supports harsher environments, which matters for industrial and automotive applications. |
| Package / Mounting | 8-Lead SOIC (Surface Mount) | 8-Lead SOIC (Surface Mount) | Both share the same SOIC-8 footprint, so board-level physical compatibility is maintained even though the electrical functions differ. |
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Full specification comparison
Use manufacturer datasheets as the final authority.
| Specification | AD847AR | AD8479BRZ |
|---|---|---|
| Part Status | Obsolete | Active |
| Base Product Number | AD847 | - |
| Amplifier Type | Standard (General Purpose) | General Purpose |
| Number of Circuits | 1 | 1 |
| Slew Rate | 300V/µs | 8V/µs |
| Gain Bandwidth Product | 50 MHz | - |
| Current - Input Bias | 3.3 µA | - |
| Voltage - Input Offset | 500 µV | 500 µV |
| Supply Current | 5.3mA | 550µA |
| Voltage - Supply Span (Min) | 9 V | - |
| Voltage - Supply Span (Max) | 36 V | - |
| Operating Temperature | -40°C ~ 85°C | -40°C ~ 125°C |
| Mounting Type | Surface Mount | Surface Mount |
| Packaging | Tube | - |
| Current - Output / Channel | 32 mA | 55 mA |
| Output Type | - | Rail-to-Rail |
| -3 dB Bandwidth | - | 130 kHz |
| Voltage - Supply Span(Min) | - | 5 V |
| Voltage - Supply Span(Max) | - | 36 V |
Frequently asked questions
What are the primary functional differences between the AD8479BRZ and the AD847AR?
The AD8479BRZ is a precision, high common-mode voltage difference amplifier designed to measure signals with very high common-mode voltages (up to ±600 V), featuring a fixed gain of 1 and excellent CMRR. The AD847AR is a high-speed, low-power operational amplifier with a 50 MHz gain-bandwidth product and 300 V/µs slew rate, intended for general-purpose signal conditioning and amplification. They serve fundamentally different roles: the AD8479BRZ is a specialized difference amplifier for high-voltage sensing, while the AD847AR is a general-purpose op-amp.
Can the AD847AR be used as a direct substitute for the AD8479BRZ in high common-mode voltage measurement applications?
No. The AD847AR is a standard operational amplifier with a maximum supply voltage of ±18 V and no integrated high-voltage input attenuation network. It cannot directly accept common-mode voltages up to ±600 V as the AD8479BRZ can. Substitution would require external precision resistor networks and careful design, and would not match the AD8479BRZ's integrated performance and safety margins.
How do the package and pinout of the AD8479BRZ and AD847AR compare?
The AD8479BRZ is offered in an 8-lead SOIC package (R-8 suffix). The AD847AR is available in an 8-lead SOIC (R-8) as well as other package options depending on grade. While both may use an 8-lead SOIC footprint, the pin functions differ: the AD8479BRZ pinout is dedicated to a difference amplifier (e.g., +IN, -IN, REF, OUT, supply pins), whereas the AD847AR follows a standard single op-amp pinout (e.g., +IN, -IN, V+, V-, OUT, NULL). Direct PCB interchange is not possible without redesign.
What are the key AC performance specifications of the AD847AR compared to the AD8479BRZ?
The AD847AR offers a gain-bandwidth product of 50 MHz and a slew rate of 300 V/µs, making it suitable for high-speed signal processing. The AD8479BRZ, as a precision difference amplifier, has a much lower bandwidth (typically 480 kHz at gain = 1) and is optimized for DC accuracy and high common-mode rejection rather than high-speed operation. The AD847AR is therefore preferred for wideband amplification, while the AD8479BRZ is preferred for precision high-voltage sensing.
What are the supply voltage requirements for each device?
The AD8479BRZ operates from dual supplies typically ranging from ±2.5 V to ±18 V (or single supply 5 V to 36 V), with the ability to handle high common-mode voltages independent of its own supply. The AD847AR operates from dual supplies of ±4.5 V to ±18 V (or single supply 9 V to 36 V). Both are compatible with standard ±15 V analog systems, but the AD8479BRZ's input common-mode range extends far beyond its supply rails.
Which device is better suited for precision current sensing in motor control or power supply applications?
The AD8479BRZ is specifically designed for high-side current sensing where the common-mode voltage can exceed the supply rails, thanks to its ±600 V common-mode input range and high CMRR (typically 90 dB at DC). The AD847AR lacks this capability and would require external level-shifting or isolation circuitry. For precision current sensing in high-voltage rails, the AD8479BRZ is the appropriate choice; the AD847AR is better suited for low-voltage signal amplification after the sensing element.
Are the AD8479BRZ and AD847AR interchangeable in terms of accuracy and offset specifications?
No. The AD8479BRZ is a precision difference amplifier with low offset voltage (typically ±0.5 mV max for the B grade) and low offset drift, optimized for DC accuracy. The AD847AR is a high-speed op-amp with offset voltage specifications in the range of a few millivolts (e.g., ±5 mV max for the A grade) and is not trimmed for the same level of DC precision. They are not interchangeable where precision DC accuracy is required.
What are the typical applications for each device?
The AD8479BRZ is typically used in high-voltage current sensing, power supply monitoring, motor control, and battery management systems where common-mode voltages exceed the supply rails. The AD847AR is used in general-purpose amplification, active filters, video and RF signal chains, and high-speed data acquisition where wide bandwidth and fast slew rate are needed. Application requirements should guide selection rather than direct substitution.