AD629 Alternatives and Equivalents: INA149 vs INA117 vs AD8479

The INA149 is generally the closest alternative to the AD629 for an SOIC-8 design, while the INA117 is an older, lower-performance option and the AD8479 is the stronger choice when a much wider common-mode range is required. However, none should be treated as an automatic replacement without checking the package, supply rails, common-mode voltage, reference-pin connections, output range and required accuracy.

Quick Answer: What Is the Best AD629 Equivalent?

For most new SOIC-8 designs, the Texas Instruments INA149 is the closest functional alternative to the Analog Devices AD629. Both are unity-gain, high-common-mode-voltage difference amplifiers with a similar eight-pin signal arrangement and 500 kHz bandwidth. The INA149 supports a ±275 V common-mode range, compared with ±270 V for the AD629, and specifies a 90 dB minimum CMRR over its rated temperature range.

The INA117 can be considered in less demanding applications or where a DIP-8 device is needed, but it is not a full performance-equivalent replacement. Its common-mode range is limited to ±200 V and its guaranteed CMRR is lower. In fact, Analog Devices describes the AD629 as an improved replacement for the INA117P and INA117KU, so that replacement relationship should not automatically be reversed.

The AD8479 is the preferred candidate when the design needs substantially more common-mode headroom. It extends the operating common-mode range to ±600 V and is listed by Analog Devices as an alternative part for new designs, but it has different bandwidth, input impedance, output behavior and error specifications.

What the AD629 Does

The AD629 is a precision, fixed-gain difference amplifier designed to measure a relatively small differential signal riding on a much larger common-mode voltage. Typical applications include high-side current sensing, battery-stack monitoring, power-supply current monitoring and motor control.

With both reference pins connected to the same low-impedance reference potential, the device provides a differential gain of one. In a conventional dual-supply circuit with the reference pins grounded, its simplified transfer function is:

VOUT = V+IN − V−IN

The important feature is not signal gain but common-mode rejection. The AD629 can operate with common-mode input voltages up to ±270 V while running from much lower local supply rails. It is available in PDIP-8 and SOIC-8 packages, operates from ±2.5 V to ±18 V supplies and has a 500 kHz small-signal bandwidth. Analog Devices currently lists the AD629 as a production device, so an alternative may be needed because of sourcing, cost, environmental range or new-design requirements rather than formal obsolescence.

AD629 vs INA149 vs INA117 vs AD8479

Values above are headline or guaranteed limits under the conditions stated in the respective manufacturer data sheets. Common-mode range and output swing vary with supply voltage, output voltage, reference voltage, temperature and grade. Always compare the full electrical-characteristics tables for the intended operating point.

INA149: The Closest General Alternative to the AD629

The INA149 is usually the first device to evaluate when replacing an AD629 in an SOIC-8 circuit. It preserves the core architecture: a precision operational amplifier combined with an integrated, laser-trimmed resistor network to produce a fixed unity differential gain and reject a large common-mode voltage.

Its ±275 V common-mode range slightly exceeds the AD629's ±270 V rating. It also offers a 500 kHz bandwidth, ±2 V to ±18 V dual-supply operation, a maximum gain error of 0.02%, a 90 dB minimum CMRR and operation specified from −40°C to +125°C. Those specifications make the INA149 attractive for industrial current sensing and motor-control designs that need a wider temperature range.

The SOIC-8 pin functions align with the AD629's basic connection scheme: reference input on pins 1 and 5, signal inputs on pins 2 and 3, negative supply on pin 4, output on pin 6, positive supply on pin 7 and no connection on pin 8. This greatly simplifies PCB evaluation, but matching pins do not by themselves guarantee a drop-in replacement.

Designers still need to compare offset error, drift, output swing, load drive, capacitive-load stability, input protection and the exact common-mode range available at the chosen supply voltage. The INA149 is also available only in SOIC-8, so it does not provide a direct package solution for an existing PDIP-8 socket.

Available INA149 Ordering Options

After choosing the INA149 electrically, select the complete ordering code according to qualification and assembly requirements. Octatronics lists the following INA149 configurations:

1. INA149AID — the standard industrial-temperature INA149 in an SOIC-8 package, suitable for evaluation, repair and lower-volume assembly requirements.
2. INA149AIDR — the SOIC-8 industrial version supplied in tape-and-reel format for automated production.
3. INA149AMDREP — an INA149-EP enhanced-product ordering option intended for designs that require an enhanced qualification flow and controlled manufacturing baseline.

The D and DR versions use the same basic INA149 function, but their packing format differs. The EP version should be selected because its qualification and documentation match the project, not simply because it appears to be a higher grade. Confirm the current data sheet, material declaration and ordering status for the exact suffix before approving it on a bill of materials.

INA117: Related to the AD629, but Not a Full Equivalent

The INA117 frequently appears in AD629 cross-reference discussions because the devices share the same basic function, unity gain and familiar eight-pin arrangement. The INA117P is offered in PDIP-8, while the INA117KU is the SOIC-8 version. It can therefore be useful in a legacy repair where physical package compatibility matters and the circuit does not approach the AD629's performance limits.

Nevertheless, calling the INA117 a direct AD629 equivalent is potentially misleading. The INA117's specified common-mode range is ±200 V, 70 V lower in each direction than the AD629. Its headline minimum CMRR is 70 dB, compared with up to 86 dB for the AD629B at 500 Hz. That difference can create a significant output error when the desired differential signal is small but the common-mode voltage is large.

The latest TI data sheet also identifies two qualified fabrication flows with different bandwidth specifications: 200 kHz for one flow and 500 kHz for the other. A robust replacement design should therefore be valid at the lower guaranteed bandwidth unless the supplied device flow is controlled.

The direction of the manufacturer's replacement statement matters here. Analog Devices calls the AD629 an improved replacement for the INA117P and INA117KU. That means an AD629 can often upgrade an INA117 application; it does not mean an INA117 automatically preserves the performance of a circuit designed around the AD629.

INA117 Package, Packing and Legacy Grade Options

INA117 ordering codes span surface-mount, through-hole and legacy metal-can configurations. They should be separated by physical package before comparing price or availability.

1. SOIC-8 options: INA117KUG4 is a green-finish SOIC ordering code; INA117KU/2K5 is the 2,500-piece tape-and-reel configuration; and INA117KU/2K5G4 combines the reel format with the G4 green-finish suffix.
2. PDIP-8 option: INA117PG4 is the through-hole plastic DIP configuration and is the most relevant INA117 option when an existing board uses an eight-pin DIP footprint.
3. Legacy TO-CAN options: INA117AM, INA117BM, INA117SM and INA117SMQ are associated with eight-pin metal TO-CAN packaging and older grade or screening structures.

Do not substitute a KU, P or M-suffix device based only on the INA117 base number. SOIC-8, PDIP-8 and TO-CAN packages are physically different. Some G4 and metal-can codes are also legacy orderables, so lifecycle, lead finish, temperature grade and screening should be confirmed against current manufacturer documentation and the requirements of the original equipment.

AD8479: The Higher-Voltage Alternative

The AD8479 is the most compelling option when ±270 V is not enough or when additional common-mode margin is desirable in a new design. It supports a ±600 V operating common-mode range, uses a fixed gain of one and operates from ±2.5 V to ±18 V supplies. The B grade specifies 90 dB minimum CMRR at ±600 V, and the device is rated from −40°C to +125°C.

It also uses the same functional SOIC-8 pin pattern as the AD629. However, the AD8479 is not simply an AD629 with a larger voltage number. Its input resistor network and input impedance are different, its small-signal bandwidth is 310 kHz, and it provides a rail-to-rail output that can swing to approximately 0.3 V from either supply rail under specified conditions. Source-impedance effects, noise and dynamic response must therefore be evaluated again.

One especially important practical consideration is power dissipation. Applying hundreds of volts to the internal input-divider network generates heat. Designers using the AD8479 near its maximum common-mode voltage should follow the junction-temperature derating guidance in the data sheet instead of considering ±600 V a condition that is automatically safe at every ambient temperature.

Are the Devices Pin-Compatible?

In their SOIC-8 versions, the AD629, INA149, INA117 and AD8479 use equivalent basic pin functions:

1. Pin 1: negative/reference-B input
2. Pin 2: inverting signal input
3. Pin 3: noninverting signal input
4. Pin 4: negative supply
5. Pin 5: positive/reference-A input
6. Pin 6: output
7. Pin 7: positive supply
8. Pin 8: no connection

Even so, a schematic and PCB review is required. Confirm the package outline, pad dimensions, reference-pin treatment and the manufacturer's instruction for pin 8. In particular, the AD629 and AD8479 data sheets instruct users to leave pin 8 open. A legacy board that grounded an unused pin should therefore be reviewed before installing a different device.

Seven Checks Before Replacing the AD629

1. Measure the real common-mode range. Include normal operation, startup, regenerative events, switching overshoot and fault conditions. An INA117 is not suitable if the circuit can exceed its ±200 V continuous input limit.
2. Check common-mode range at the actual supply and reference voltage. The headline voltage is normally specified with particular dual supplies. Single-supply operation and a shifted reference can substantially reduce the usable positive or negative common-mode range.
3. Calculate the CMRR error. A lower CMRR can dominate the measurement error when hundreds of common-mode volts surround a millivolt-level signal. Check both dc CMRR and CMRR at the switching or interference frequency.
4. Verify output swing and ADC compatibility. Make sure the output remains inside the linear range of both the amplifier and the following ADC across tolerances, transients and temperature.
5. Review source and shunt resistance. Extra resistance in either input path disturbs the internal resistor-network balance and reduces common-mode rejection. Large shunt resistance can also introduce gain error through input loading.
6. Compare dynamic behavior. Bandwidth alone is not enough. Review slew rate, settling time, capacitive-load stability, noise and common-mode step response for PWM motor drives and switching power systems.
7. Prototype and validate. Simulate where manufacturer models are available, then test the replacement across supply, temperature, load and common-mode extremes before production approval.

Common-Mode Capability Is Not Galvanic Isolation

The AD629, INA149, INA117 and AD8479 can measure signals riding on high common-mode voltages, but they do not create an isolation barrier. Their input and output circuits still share a conductive relationship through the device. If the design needs reinforced insulation, safety isolation, ground-loop interruption or protection between hazardous-voltage and user-accessible domains, use a properly rated isolated amplifier, isolated ADC or isolated current-sensing solution instead.

This distinction is especially important in traction inverters, mains-connected power conversion, industrial drives and high-voltage battery systems. A component's common-mode input rating must never be treated as a substitute for creepage, clearance and certified isolation requirements.

Understanding AD629 Ordering Codes

Some apparent “equivalents” are actually ordering variants of the same AD629. For example, AD629BRZ-R7 is not a different electrical substitute: it is a B-grade AD629 in an SOIC package supplied in tape-and-reel form. The ordering code can be read in several parts:

1. A or B identifies the electrical performance grade. The B grade provides tighter offset-drift, gain-nonlinearity and CMRR limits.
2. R identifies the eight-lead SOIC package in these ordering codes.
3. Z identifies a lead-free/RoHS-compatible orderable version.
4. R7, RL, REEL7 or REEL identifies a tape-and-reel shipping format. Reel diameter and standard packing quantity should be confirmed for the exact order code.

When sourcing a replacement, separate three questions: Is it the same base device? Is it the same electrical grade? Is it supplied in the package and packing format required by assembly? A reel suffix can matter to purchasing and manufacturing without changing the circuit function.

AD629B High-Accuracy SOIC-8 Variants

Use a B-grade device when the design relies on the tighter AD629B common-mode rejection and drift limits. The available Octatronics product pages cover both current lead-free codes and legacy reel nomenclature:

1. AD629BRZ — B-grade, lead-free SOIC-8 standard order code.
2. AD629BRZ-R7 — B-grade, lead-free SOIC-8 in the R7 tape-and-reel format.
3. AD629BRZ-RL — B-grade, lead-free SOIC-8 using the RL reel order code.
4. AD629BR-REEL7 — B-grade SOIC-8 using the legacy REEL7 nomenclature.
5. AD629BR-REEL — B-grade SOIC-8 using the legacy REEL nomenclature.

AD629A General-Purpose SOIC-8 Variants

The A-grade order codes retain the same AD629 architecture and ±270 V common-mode capability but have looser guaranteed precision limits than the B grade. Available internal product references include:

1. AD629ARZ-R7 — A-grade, lead-free SOIC-8 in the R7 tape-and-reel format.
2. AD629ARZ-RL — A-grade, lead-free SOIC-8 using the RL reel order code.
3. AD629AR-REEL7 — A-grade SOIC-8 using the legacy REEL7 nomenclature.
4. AD629AR-REEL — A-grade SOIC-8 using the legacy REEL nomenclature.

For a new bill of materials, the Z-suffix order codes are normally the clearer starting point when lead-free compliance is required. Legacy non-Z codes may still be relevant for repair, approved-vendor-list continuity or form-fit-function replacement, but material compliance and lifecycle status must be checked rather than inferred from the base part number.

Which Device Should You Choose?

1. Choose INA149 when you need the closest general SOIC-8 alternative, ±275 V common-mode capability, 500 kHz bandwidth and an extended +125°C specified temperature range.
2. Choose INA117P only when a PDIP-8 legacy replacement is important and the application safely fits within its lower common-mode, CMRR and bandwidth limits.
3. Choose AD8479 for a new SOIC-8 design that requires up to ±600 V common-mode operation and can accommodate its different dynamic and input characteristics.
4. Keep the AD629 when the existing design depends on its characterized behavior, qualification history or PDIP availability and there is no strong reason to change.

Frequently Asked Questions

Is the INA149 a direct replacement for the AD629?

It is the closest general candidate for many SOIC-8 applications, and the basic pin functions align. However, it should not be approved as a direct replacement until the complete electrical specifications have been checked and the circuit has been validated.

Can the INA117 replace the AD629?

Only in applications that remain within the INA117's limits. Its ±200 V common-mode range and lower minimum CMRR make it a performance downgrade from the AD629 in important areas. It is not suitable when the circuit relies on the AD629's full ±270 V capability.

What is the best AD629 replacement for a DIP-8 board?

The INA117P is available in PDIP-8 and has matching basic pin functions, but its performance is lower. If the original AD629 PDIP version remains available, retaining the AD629 may be safer. Otherwise, evaluate the actual voltage and error requirements before using the INA117P or redesigning with an SOIC adapter.

Is AD629BRZ-R7 an AD629 equivalent?

It is not a different equivalent part. It is an orderable version of the AD629B in SOIC packaging and tape-and-reel format.

Does the AD8479 provide electrical isolation?

No. Its ±600 V common-mode rating allows high-voltage differential measurement without galvanic isolation, but it does not provide a certified isolation barrier.

Are these amplifiers suitable for single-supply operation?

They can be used in single-supply configurations when the reference pins and output bias are designed correctly. The available common-mode input range and output swing will differ from the headline dual-supply specifications, so the relevant data-sheet equations and curves must be used.

Conclusion

The INA149 is usually the best starting point when engineers ask for an AD629 equivalent, particularly for an SOIC-8 industrial design. The INA117 is better described as a related legacy alternative with lower common-mode and rejection performance, while the AD8479 is a higher-voltage redesign option rather than a like-for-like substitute.

No cross-reference table can replace application-level verification. Before changing the device, compare the exact grade and package, calculate errors at the real common-mode voltage and frequency, examine supply and reference conditions, and validate the circuit under worst-case operating conditions.