INA129U/2K5 - Precision Low Power INA, SOIC-8 | Texas Instruments
MPN: INA129U/2K5 ✓ Active| Qty | Unit Price | Extended |
|---|---|---|
| 1 | $6.43 | $6.43 |
| 10 | $5.79 | $57.90 |
| 100 | $4.51 | $451.00 |
| 500 | $3.78 | $1,890.00 |
| 1,000 | $3.32 | $3,320.00 |
| 2,500 | $2.99 | $7,475.00 |
INA129U/2K5 Overview
An instrumentation amplifier is a precision differential amplifier with very high input impedance on both inputs, a defined and stable gain set by one external resistor, and exceptionally high common-mode rejection. The INA belongs to the family of analog front-end ICs that sit between a sensor (bridge, thermocouple, biopotential electrode) and an ADC. The category hierarchy is: instrumentation amplifier -> differential amplifier -> operational amplifier -> analog IC -> semiconductor. The three-op-amp topology isolates the input signal from the gain-setting resistor network, allowing tiny differential signals (often microvolts) to be amplified cleanly in noisy industrial environments.
Key features of the INA129U/2K5 include wideband operation up to 1.3 MHz (G = 1) with 200 kHz bandwidth even at G = 100, a 4 V/µs slew rate, ±2.25 V to ±18 V dual-supply operation (±2.25 V minimum; typically ±15 V in transducer systems), input protection to ±40 V, and a quiescent current of only 700 µA typical. The exposed SO-8 package simplifies reflow assembly on standard 8-pin SOIC land patterns identical to the INA128, AD620, and other pin-compatible INAs.
The current-feedback input stage keeps bandwidth flat across the full gain range, an advantage over voltage-feedback INAs that lose bandwidth at high gain. The INA129's gain equation G = 1 + 49.4kΩ/RG matches the AD620, allowing direct drop-in migration from legacy designs. The combination of low noise, low drift, and high CMRR makes the INA129U/2K5 well-suited for strain-gauge bridges, weigh scales, thermocouple amplifiers, medical instrumentation (ECG/EEG front-ends), and industrial process-control analog inputs.
Typical applications include weigh scales and load-cell signal conditioning, ECG and biomedical front-ends, thermocouple and RTD pre-amplification, and industrial 4-20 mA loop readouts. Place the gain-setting resistor close to pins 1 and 8, and use 0.1 µF ceramic bypass capacitors on both supply pins to preserve the 120 dB CMRR across frequency. This page synthesizes distributor pricing, drop-in alternatives, and practical design notes not found in the manufacturer datasheet.
Drop-in alternatives for INA129U/2K5 — same package, pin-to-pin compatible. Different-package parts requiring PCB rework are excluded.
Quick Comparison Tool — Select alternative parts for side-by-side comparison:
INA128U/2K5
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INA128UA/2K5
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INA121UAG4
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AD620ANZ
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View Datasheet →INA333AIDR
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INA118PB
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INA129U/2K5 Maximum Ratings & Electrical Characteristics
| Manufacturer | Texas Instruments |
| Product Type | Instrumentation Amplifier (INA) |
| Series | INA12x (INA128 / INA129) |
| Number of Channels | 1 |
| Topology | 3-Op-Amp, current-feedback input |
| Package / Case | 8-pin SOIC (SO-8) |
| Mounting Type | Surface Mount |
| Supply Voltage (Dual) | ±2.25 V to ±18 V |
| Quiescent Current | 700 µA typical |
| Input Offset Voltage (max) | 50 µV |
| Offset Drift (max) | 0.5 µV/°C |
| Input Bias Current (max) | 5 nA |
| CMRR (min) | 120 dB (at G = 100) |
| Bandwidth (G = 1) | 1.3 MHz |
| Bandwidth (G = 100) | 200 kHz |
| Slew Rate | 4 V/µs |
| Gain Range | 1 V/V to 10,000 V/V |
| Gain Equation | G = 1 + 49.4kΩ / RG (AD620-compatible) |
| Input Protection | ±40 V |
| Operating Temperature | -40 °C to +85 °C |
| Reel Quantity | 2,500 (per /2K5 suffix) |
| RoHS | Compliant |
INA129U/2K5 Pin Configuration
| Pin 1 | RG — Gain-setting resistor pin (connect external resistor to pin 8) |
| Pin 2 | -IN — Inverting input |
| Pin 3 | +IN — Non-inverting input |
| Pin 4 | V- — Negative supply voltage |
| Pin 5 | REF — Output reference (level-shift output; normally tied to GND for dual supply) |
| Pin 6 | OUTPUT — Amplifier output |
| Pin 7 | V+ — Positive supply voltage |
| Pin 8 | RG — Gain-setting resistor pin (connect external resistor to pin 1) |
Typical Applications
INA129U/2K5 is suitable for 6 applications: Weigh Scale / Load Cell Signal Conditioning, ECG and Biomedical Front-End, Thermocouple and RTD Temperature Amplifier, Industrial 4-20 mA Loop Readout, Strain-Gauge Bridge Amplifier, Audio Precision Preamplifier.
Weigh Scale / Load Cell Signal Conditioning
The INA129U/2K5 is the canonical load-cell amplifier for industrial weigh scales. Its 120 dB minimum CMRR at G=100 rejects 50/60 Hz mains pickup that couples into long load-cell cables, while the 50 µV maximum offset and 0.5 µV/°C maximum drift maintain calibration accuracy across the -40 °C to +85 °C industrial range. The current-feedback input stage keeps bandwidth flat (~200 kHz) even at G=100, allowing fast settling for batch-weighing applications. Place the gain resistor close to pins 1 and 8 and add 0.1 µF ceramic bypass on both supply rails to preserve the 120 dB CMRR figure. The SOIC-8 footprint is pin-compatible with AD620, enabling direct migration.
Recommended
ECG and Biomedical Front-End
The INA129U/2K5 is widely used as the first gain stage in ECG, EEG, and EMG front-ends. Its 5 nA maximum input bias current is well below typical skin-electrode impedance levels, preventing polarization of Ag/AgCl electrodes. The 120 dB minimum CMRR rejects common-mode mains interference when set to G = 10 with right-leg-drive feedback, while the 50 µV maximum offset contributes negligible baseline wander. The 1.3 MHz bandwidth captures high-frequency QRS complexes without distortion. Designers should add ESD protection (TVS arrays) and AC coupling at the inputs per AAMI EC11/IEC 60601-1 safety standards. The SOIC-8 footprint supports compact wearable designs.
Recommended
Thermocouple and RTD Temperature Amplifier
The INA129U/2K5 amplifies the microvolt-level outputs of K-type, J-type, and S-type thermocouples with 50 µV offset accuracy that adds less than 1 °C error to cold-junction-compensated readings. The high CMRR rejects 50/60 Hz thermocouple-loop pickup in industrial furnaces. For RTD-based temperature sensing, the INA129's 5 nA bias current minimizes self-heating errors on PT100/PT1000 elements. The ±2.25 V to ±18 V supply range allows operation from standard ±5 V or ±15 V industrial rails. Use the REF pin (pin 5) to level-shift the output for single-supply ADC interfaces; the gain equation G = 1 + 49.4kΩ/RG simplifies resistor selection for the 1 mV/°C K-type output range.
Recommended
Industrial 4-20 mA Loop Readout
The INA129U/2K5 reads the differential voltage across a current-sense resistor in 4-20 mA HART-protocol loops. Its ±40 V input protection survives field wiring faults and accidental mains contact, critical for IEC 61000-4 compatibility in process-control installations. The 120 dB CMRR rejects ground-loop noise between field transmitters and the control cabinet, while the 1.3 MHz bandwidth supports HART 1200 bps FSK modulation pass-through without attenuation. The SOIC-8 small footprint enables channel-density multi-rail acquisition cards. Power the INA129 from the same ±15 V supply that powers downstream ADCs, simplifying the BOM.
Recommended
Strain-Gauge Bridge Amplifier
The INA129U/2K5 is ideal for amplifying full-bridge and half-bridge strain-gauge transducers in structural-health monitoring and pressure-sensor applications. The 120 dB CMRR ensures bridge common-mode voltage (typically 2.5 V or 5 V) is rejected to better than 1 µV, while the 50 µV offset does not compromise the millivolt-level strain signals. The 4 V/µs slew rate preserves dynamic response for vibration and impact testing. The SOIC-8 footprint and external gain resistor allow precise gain calibration per transducer sensitivity (typically 1-4 mV/V). Place a 100 nF ceramic bypass on each supply pin and keep the gain resistor within 5 mm of pins 1 and 8 to maintain CMRR.
Recommended
Audio Precision Preamplifier
The INA129U/2K5 functions as a precision microphone preamp and line-level instrumentation preamp in professional audio equipment. The 1.3 MHz bandwidth and 4 V/µs slew rate support full 20 Hz-20 kHz audio bandwidth with low distortion. The 50 µV offset is inaudible in typical microphone gain (G = 100), and the 120 dB CMRR rejects ground-loop hum in balanced audio cable runs. The ±18 V maximum supply accommodates ±15 V professional audio rails. Use the REF pin to bias the output to mid-rail for single-supply ADC interfacing in digital mixers. Designers should add RF input filtering and ESD protection per IEC 61000-4-2 for stage-grade equipment.
Recommended
Recommended Products Summary
Engineering reference data for INA129U/2K5 — comparison, design guidance, and compliance information.
Selection Guide
Comparison with Alternatives
| Parameter | This Product | INA128U/2K5 | INA128UA/2K5 | AD620ANZ | INA333AIDR |
|---|---|---|---|---|---|
| Brand | Texas Instruments | Texas Instruments | Texas Instruments | Analog Devices | Texas Instruments |
| Package | SOIC-8 (narrow) | SOIC-8 (narrow) | SOIC-8 (Wide) | SOIC-8 (narrow) | MSOP-8 |
| Topology | 3-Op-Amp, current-feedback | 3-Op-Amp, current-feedback | 3-Op-Amp, current-feedback | 3-Op-Amp, current-feedback | 3-Op-Amp, zero-drift chopper |
| Input Offset Voltage (max) | 50 µV | 50 µV | 50 µV | 50 µV | 25 µV (typ) |
| CMRR (min) | 120 dB (G=100) | 120 dB (G=100) | 120 dB (G=100) | 100 dB (G=1-1000) | 100 dB |
| Bandwidth (G=100) | 200 kHz | 200 kHz | 200 kHz | 120 kHz | 3.5 kHz |
| Slew Rate | 4 V/µs | 4 V/µs | 4 V/µs | 1.2 V/µs | 0.16 V/µs |
| Supply Voltage (Dual) | ±2.25 V to ±18 V | ±2.25 V to ±18 V | ±2.25 V to ±18 V | ±2.3 V to ±18 V | +1.8 V to +5.5 V (single supply) |
| Gain Equation | G = 1 + 49.4kΩ/RG (AD620-compatible) | G = 1 + 50kΩ/RG (industry std) | G = 1 + 50kΩ/RG (industry std) | G = 1 + 49.4kΩ/RG (same) | G = 1 + 100kΩ/RG |
Key Differentiators
- AD620-compatible gain equation for direct legacy migration (vs INA128U/2K5)
- Higher CMRR than AD620 for industrial noise environments (vs AD620ANZ)
- Current-feedback input stage maintains bandwidth at high gain (vs INA333AIDR (zero-drift))
Design Notes
Place the gain-setting resistor RG within 5 mm of pins 1 and 8 to minimize parasitic capacitance that degrades CMRR at high frequencies. Use 0.1 µF ceramic bypass capacitors on both V+ (pin 7) and V- (pin 4), positioned within 3 mm of the supply pins. Route input traces as a matched differential pair with guard traces tied to REF potential (pin 5) to reduce common-mode pickup on long sensor cables.
The REF pin (pin 5) is the output common-mode reference and must be driven from a low-impedance source. For dual-supply operation, tie REF directly to ground. For single-supply operation, drive REF from a buffered mid-rail (e.g., a resistor divider with 10 µF bypass) to level-shift the output swing above ground. Driving REF with high impedance introduces common-mode noise and degrades the 120 dB CMRR figure.
Do not exceed the ±40 V input protection rating; in industrial installations, add external TVS diodes or spark gaps for IEC 61000-4-5 surge compliance. Do not connect input signals before power is applied - the input protection clamps can forward-bias and damage downstream circuitry. Use the correct gain-resistor package (typically 0805 or 0603) with 0.1% tolerance for gain accuracy; 1% resistors introduce 1% gain error that propagates to system calibration.
Compliance Information
RoHS compliant per TI product page. Not AEC-Q100 qualified; for automotive applications consider INA129-Q1. Lead-free SOIC-8 package with NiPdAu lead finish.
