When an Analog Devices AD620 precision instrumentation amplifier experiences extended lead times, the search for alternatives almost always starts in the wrong place: the footprint. Nearly every classic instrumentation amplifier in this class ships in an 8-pin package with the gain resistor (RG) strapped across pins 1 and 8, which makes a dozen parts from four vendors look like interchangeable options. They are not.
The gain network that sets your transfer function lives inside the die, and it changes from part to part. Swap the amplifier without changing the external resistor and the circuit still works and still passes a smoke test, but amplifies by the wrong number. This guide covers which alternates preserve your gain math, which ones force a BOM change, and how to tell the difference before the board comes back for a redesign.
Next step: Check current AD620 availability and distributor coverage on Findchips
Why Instrumentation Amplifier Alternates Appear Interchangeable
The single-resistor gain architecture is the reason the AD620 is so pleasant to design with and so treacherous to substitute. In contrast to a conventional non-inverting op amp, which uses two resistors, the AD620 requires just one external resistor, one equation and one part number in the BOM. The pinout convention is close to universal across the category: inputs on pins 2 and 3, reference on pin 5, output on pin 6, and the RG across pins 1 and 8. A cross-reference search tool that matches on package, pin count and function will return a long list of candidates, and every one of them will look like a drop-in replacement.
The problem is that pin compatibility and gain compatibility are two separate claims, and only one of them is visible from the outside of the part. The internal resistor that pairs with your external RG is a design choice each vendor made independently. Some vendors deliberately matched the AD620 value to win exactly this kind of substitution. Others picked a different value to optimize for supply rail, noise, or drift. Both decisions are defensible. Only one of them lets you reuse your resistor, however.
Next step: Compare instrumentation amplifier stock across distributors on Findchips
The Gain Network is Inside the Part Number
Here is the comparison that matters when you are evaluating AD620 alternatives. Every one of these parts uses the same single resistor scheme, and four of the six produce a different gain from the same resistor value.
| Part | Gain equation | Gain range | Supply | Reuses an AD620 gain resistor? |
|---|---|---|---|---|
| AD620 | G = 1 + (49.4k / RG) | 1 to 10,000 | ±2.3V to ±18V | Reference part |
| LT1167 | G = 1 + (49.4k / RG) | 1 to 10,000 | ±2.3V to ±18V | Yes, by design |
| INA826 | G = 1 + (49.4k / RG) | 1 to 1,000 | 2.7V to 36V single | Yes, within its gain range |
| INA333 | G = 1 + (100k / RG) | 1 to 1,000 | 1.8V to 5.5V single | No, roughly double the gain |
| AD8422 | G = 1 + (19.8k / RG) | 1 to 1,000 | ±2.5V to ±18V | No, roughly 40 percent of the gain |
| INA126 | G = 5 + (80k / RG) | 5 to 10,000 | ±1.35V to ±18V | No, and the minimum gain is 5 |
The last column assumes the starting point most AD620 designs from Analog Devices share: split supplies, with gain set by a single external resistor. If your circuit already runs on a single supply at 5V or below, the ranking shifts, and the INA333 moves from redesign to a live candidate on its own merits.
Read the last column as a rework estimate. An AD8422 swap costs you that plus a resistor value change and a bench check of the new gain. The INA333 and INA126 from Texas Instruments sit further out than either: the INA333 tops out at a 5.5V single supply, and the INA126 has a gain floor of 5, so neither one can be reached from a typical split supply AD620 circuit by changing a resistor at all.
Next step: Search AD620 alternatives by manufacturer and package on Findchips
What Changes Beyond Gain: CMRR, Supply Rails, and Noise
Gain is the failure that bites first, but it is rarely the only one. Three other axes move when you change parts in this category.
Supply architecture is the hardest constraint to negotiate. The INA333 is a single-supply part topping out at 5.5V, so it cannot stand in for an AD620 running on split rails without a redesign of the reference and the input common-mode range. The INA826 tolerates a wide single-supply span up to 36V, which makes it the more flexible substitute when your rails are already fixed.
Common-mode rejection ratio (CMRR) generally improves on the newer parts, and that is not free. Higher CMRR in this category typically comes from tighter internal trimming, which shows up as a different price band and sometimes a different lead time profile than the part you are replacing. Zero-drift parts like the INA333 trade low-frequency noise and offset drift for higher broadband noise, which matters if your sensor bandwidth extends past a few kilohertz.
Output swing behavior also differs. Rail-to-rail output parts and classic bipolar output parts do not clip at the same place, so a substitution that looks clean at nominal signal levels can saturate at the top of your measurement range.
Next step: Check lead time and pricing signals across in-amp manufacturers on Findchips
Which AD620 Alternatives are True Drop-ins?
Sort the candidates into three buckets and the sourcing decision gets much faster.
True drop-in means the same gain equation, compatible supply, and the same pinout. The LT1167 is the clearest case here: It was built to be pin and gain compatible with the AD620, and in most designs it is a straight swap subject to noise and supply verification. Treat it as your first call when the AD620 tightens.
Resistor change only means the pinout and supply work but the gain equation differs. The AD8422 falls here for split supply designs, and the swap costs you one resistor value and a bench verification of the new gain. This is a real option when the schedule pressure is on the amplifier and not on the passive.
Redesign means the supply architecture, gain floor, or output stage does not match. The INA333 and INA126 land here relative to a typical split-supply AD620 circuit. These are excellent parts chosen on their own merits at design time and poor emergency substitutes mid build.
Next step: Compare LT1167 and AD8422 availability side by side on Findchips
How to Qualify a Second Source Without a Board Respin
Start from your gain resistor, not from your amplifier. Write down the gain your circuit actually needs, then solve each candidate equation for RG at that gain and check whether the result is a standard value in a tolerance you can buy. A candidate that needs a 1 percent oddball resistor to hit your gain is a candidate that will cause a second sourcing problem later.
Confirm the input common mode range at your actual reference voltage rather than at the datasheet headline. In-amp common mode range is a function of gain, supply and reference pin voltage together, and the typical failure is a part that is perfectly valid on paper and starved at your operating point.
Qualify the alternate on the same board revision if you can. Because the pinouts match, a resistor swap and a part swap on an existing assembly gets you most of the way to a qualification without a new spin, which is the practical argument for keeping one resistor change alternate on the AVL alongside the true drop-in.
Next step: Build a cross-reference shortlist for your in-amp on Findchips
Frequently Asked Questions
Is the LT1167 a direct replacement for the AD620?
The LT1167 uses the same gain equation and the same pinout as the AD620, so in most designs it is a direct swap that reuses your existing gain resistor. Verify supply range and noise performance against your specific signal chain before committing.
Can I use an INA333 in place of an AD620?
Usually not without a redesign. The INA333 is a single-supply part limited to 5.5V and uses a 100k internal gain network, so it produces roughly double the gain from the same resistor and cannot support a split-supply AD620 circuit as built.
Why does my gain change when I swap instrumentation amplifiers with the same pinout?
Because the gain resistor is only half of the network. The other half is an internal resistor fixed by the manufacturer, and its value differs by part: 49.4k on the AD620 and LT1167, 100k on the INA333, 19.8k on the AD8422. Same external resistor, different gain.
What is the fastest AD620 alternate to qualify when lead times stretch?
The LT1167 for a no-change swap, and the AD8422 when you can accept a single resistor value change. Both keep the existing pinout, so qualification can usually happen on the current board revision.
Next step: Check real-time availability for every part in this comparison on Findchips
The Sourcing Takeaway
Instrumentation amplifier substitution is not a footprint problem, and treating it as one is how a swap that passed cross-reference ends up failing calibration. The compatibility that decides your second source is the internal gain network, and it is invisible to every tool that matches on package and function.
Sort your AD620 alternatives into drop-in, resistor change, and redesign before the shortage arrives, and keep at least one of the first two qualified on your AVL. The work takes an afternoon when you are not under pressure, and it’s well worth the time to avoid a respin.
Next step: Start your AD620 alternatives search on Findchips