INA128U
Texas Instruments
MOQ 1 · Tube · RoHS · EIA-481 · DAP/DDP · T/T
Technical specifications
| Parameter / Attribute | Specification / Value |
|---|---|
| Mounting | Surface Mount |
| Amplifier type | Instrumentation |
| Voltage - input offset | 10 µV |
| Voltage - supply span | 4.5 V |
| Current - supply | 700µA |
| Current - input bias | 2 nA |
| Current - output (Channel) | 15 mA |
| Operating temperature | -40°C~85°C |
| -3db bandwidth | 1.3 MHz |
| Package | Tube |
| Slew rate | 4V/µs |
| Case | 8-SOIC (0.154\", 3.90mm Width) |
| Number of circuits | 1 |
Need Stock or a Drop-in Second-Source for INA128U?
Package: DIP-8 / SOIC-8 · Pin-compatible replacements with immediate Shenzhen spot stock
The AD620 is the instrumentation amplifier of medical front ends, load cells, thermocouples and every bridge sensor that needed clean differential gain from an eight-pin body - one external resistor sets gains from 1 to 10000, and the part has been the reference point of its class since the 1980s. Its replacement story is unusually polite: the AD8221 was introduced as the higher-performance pin-compatible successor with the SAME gain formula, so the gain resistor carries over; the AD623 opens the single-supply world at lower cost with a DIFFERENT gain formula, so the resistor does not carry over. The family rule for repair is one sentence: the socket is generous, the gain math is not.
Verified Pin-Compatible Replacements (3 verified alternatives)
The Documented Successor with the Same Gain Resistor
Shenzhen Spot Stock (24-48h Dispatch)
Pin-compatible with the same gain transfer function (49.4k divided by RG, plus one): better offset (about 60uV against 125uV), better CMRR (130dB at G=1000 class against 110), higher input impedance and lower bias current - with a slightly lower bandwidth at high gain.
Same +/-2.3V to +/-18V dual-supply envelope.
The Single-Supply Cousin - Different Gain Math
Shenzhen Spot Stock (24-48h Dispatch)
The single-supply member: 2.7V to 12V single or dual rails, rail-to-rail output, hundreds of microamps of quiescent current - with the gain resistor chosen by a DIFFERENT constant (100k-based against the 49.4k of the AD620 family).
The reason it exists: battery and 3.3V/5V systems where the dual-supply classics do not fit.
The Other Classic of the Socket
Shenzhen Spot Stock (24-48h Dispatch)
The Burr-Brown member of the classic eight-pin instrumentation-amplifier convention: single gain resistor, similar class, widely cross-referenced with the AD620 in instrument designs.
Dual-supply class per the family.
Buyer & Quality Checklist for Sourcing Alternatives
- The gain resistor is part of the part number: 49.4k/RG+1 for the AD620/AD8221 family, 100k/RG+1 for the AD623 - a substitution that keeps the resistor keeps the socket and changes the gain. Recompute or measure; never assume.
- CMRR is why this class exists: bridge and thermocouple front ends live on rejection of common-mode noise. Substituting down the CMRR ladder (AD623 at about 90dB against the AD8221s 130dB class) trades exactly the specification the circuit was designed around.
- Single-supply substitutes belong where the rails are single: fitting a dual-supply classic into a 5V system or the reverse is a topology question first, an amplifier question second.
- The gain range ceilings differ (AD620 to 10000, AD8221 documented to 1000): designs at the top of the range should verify the exact configuration before a substitute.
- Offset trimming discipline: after any substitution, re-zero at the operating temperature - the old trim was hiding the performance of the old part, not calibrating the circuit.
- Input protection: these front ends see sensors, and sensors see the world - check the input network against the absolute maximums when repairing, because most dead instrumentation amplifiers died of an input event, not of age.
Frequently Asked Technical Questions
Q: Is AD8221 a drop-in replacement for AD620?
A: Yes - pin-compatible with the same gain formula (same RG value carries over) and improved offset, CMRR and input characteristics. The documented gain ceiling differs (1000 against 10000), so verify configurations at the extreme top of the range.
Q: Can I use AD623 instead of AD620?
A: The socket accepts it and single-supply systems often benefit, but the gain formula differs (100k against 49.4k) and the noise floor is several times higher - recompute the gain and check whether the design was built around low-level precision before substituting.
Q: Why does my replaced instrumentation amp read the wrong gain?
A: The families share the eight-pin socket and not the gain arithmetic: identical RG values mean different gains across AD620, AD623 and the TI row. Recalculate from the new part datasheet or measure the actual gain with a known input.