MAX6675 vs MAX31855 and MAX31856: migrating off the obsolete K-type converter (2026)
The Maxim (Analog Devices) MAX6675, the cold-junction-compensated K-type thermocouple-to-digital converter in the 8-pin SO package, is obsolete: ADI names it obsolete in its own knowledge base and points to the MAX31855 and MAX31856 as the replacements. Engineers search max6675 vs max31855, not "obsolete," so this page compares the MAX6675 against the two Maxim/ADI successors it migrates to: the MAX31855 (co-equal target) and the MAX31856 (universal-input). Neither successor is a drop-in. The MAX31855 tops out at 3.6V where the MAX6675 tolerates 5.5V, returns 14-bit where the MAX6675 returns 12-bit, and uses a different SPI read format, so a 5V rail and the read code do not carry over. These are suggested candidates to validate in your own design, not drop-in equivalents.
Status // The part in question
Lifecycle status
The MAX6675 is obsolete, stated by the manufacturer. ADI knowledge base article KA-06721, "What is Maxim's best alternative to obsolete part MAX6675?", states verbatim that "MAX31855/MAX31856 are the replacement parts for obsolete part number MAX6675." Distributor listings corroborate with "discontinued" flags.
The useful move is to sequence the migration, not chase last stock. A last-time-buy defers the work but does not remove it: moving to the MAX31855 or MAX31856 is a requalification (new supply rail, new output word, new firmware), not a relabel, so budget it either way.
Current stock, broker availability and last-time-buy terms are dated data for the email, not this page.
Candidates // Why these
The candidate set
Two Maxim/ADI successors, each with the fit-catch to validate in your own design. The MAX6675 core, for reference: a cold-junction-compensated K-type-only converter, 12-bit result over 0 to +1024°C, 3.0V to 5.5V supply, read-only SPI with a dedicated read format, in an 8-pin SO package.
Catch: a requalification, not a drop-in. The part max6675 vs max31855 searches, and the one Adafruit sells as the "MAX6675 upgrade." It tops out at 3.6V, so a 5V MAX6675 board cannot take it without dropping the rail; it returns 14-bit over -200 to +1350°C and uses a different SPI read format that shares no code with the MAX6675. Re-do the rail, the level-shifting and the read routine.
Catch: a broader migration. The go-forward part when you need more than K-type, it accepts eight thermocouple types. But it has more configuration registers than either part, so the SPI transaction set and firmware grow, not shrink. Design it in as a new part.
Named to redirect: the MAX31865 (an RTD, PT100/PT1000, converter), the DS18B20 (a 1-Wire silicon digital temperature sensor) and the AD8495 (an analog K-thermocouple amplifier with a voltage output and no digital interface) appear in the same searches, but each is a different sensor or interface choice, not a MAX6675 migration, see the FAQ.
Identity // The read is the tell
Same function, not the same read
A distributor cross-reference filters by function, thermocouple type and interface, so it returns all three parts as matches. What it cannot filter on is the supply rail, the resolution and the SPI read format, and those are what actually decide the migration.
MAX6675 baseline vs each successor, axis by axis · the migration is what each row changes, not the part number
Read it by row: a package match on the MAX31855 passes a footprint check while the rail and the read word, the parts that actually break, still change. The MAX31856 grows to eight thermocouple types but changes the footprint too. Every migration is a hardware and firmware change, not a relabel.
Same function, not the same read. The supply rail and SPI read/register format change on both successors, suggested candidates to validate in your own design, not drop-in equivalents.
Parametrics // Side by side
Comparison table
| MAX6675 (obsolete) | MAX31855 | MAX31856 | |
|---|---|---|---|
| Vendor | Maxim / ADI | Maxim / ADI | Maxim / ADI |
| Lifecycle | Obsolete (ADI KB KA-06721) | Current (ADI-named) | Current (ADI-named) |
| Supply rail | 3.0V to 5.5V | 3.3V (3.6V max) | 3.3V |
| Resolution | 12-bit | 14-bit | 19-bit |
| Temp range | 0 to +1024°C | -200 to +1350°C | up to +1800°C, type-dependent |
| Thermocouple types | K only | One per chip (K = MAX31855K) | K/J/N/S/T/E/R/B |
| SPI interface | Read-only, dedicated format | Different register/read format, fault detection | SPI, multiple config registers |
| Package | 8-pin SO | 8-pin SO | 14-pin TSSOP |
The load-bearing rows are the supply rail and the SPI read/register format: neither successor takes a 5V rail or keeps the MAX6675's read word, so every migration is a hardware and firmware change, not a relabel. Lifecycle and electrical figures are vendor-reported, not independently audited.
FAQ // Frequently asked
Frequently asked questions
Is the MAX6675 obsolete or still in production?
The MAX6675 is obsolete. Analog Devices names it obsolete in knowledge base article KA-06721 and states the MAX31855 and MAX31856 are the replacement parts. There is no single drop-in; both successors are suggested candidates to validate, not like-for-like parts, because each changes the supply rail, the output word or the SPI read format.
Can I replace a MAX6675 with a MAX31855, is it a drop-in?
No, the MAX31855 is not a drop-in for the MAX6675; it is a requalification. Its supply tops out at 3.6V, so a MAX6675 board running at 5V cannot take it without dropping the rail; it returns a 14-bit result where the MAX6675 returns 12-bit, adds open/short/ground fault detection, and uses a different SPI read/register format that shares no code with the MAX6675. Adafruit sells its MAX31855 breakout as the "MAX6675 upgrade," but plan the rail, the level-shifting and the read routine as new work.
What is the difference between the MAX6675, MAX31855 and MAX31856?
The difference is the supply rail, the resolution and the range of thermocouples, not the basic function. All three convert a thermocouple to a digital value over SPI, but the MAX6675 is K-type only, 12-bit, and tolerates up to 5.5V; the MAX31855 is a single-type-per-chip part (K = MAX31855K), 14-bit, 3.3V with a 3.6V ceiling and fault detection; and the MAX31856 accepts eight thermocouple types (K/J/N/S/T/E/R/B) through configuration registers. Each uses a different SPI read format, so the read code does not carry across.
How do I tell a MAX6675 and a MAX31855 apart in the same circuit or code?
By the SPI read: the MAX6675 returns a 12-bit temperature in a fixed read-only format, while the MAX31855 returns a wider 14-bit result with open/short fault bits in a different layout. Code written to decode the MAX6675 word will misread a MAX31855, so the two are distinguishable, and not interchangeable, at the read routine.
MAX6675 vs MAX31865 vs DS18B20, which do I use?
These solve different sensing problems, so the choice is sensor selection, not a MAX6675 migration. The MAX31865 is an RTD (PT100/PT1000) converter, a different sensor type; the DS18B20 is a 1-Wire silicon digital temperature sensor with a limited range, not a thermocouple part; and the AD8495 is an analog K-thermocouple amplifier with a voltage output and no digital interface. If you are migrating an existing K-type MAX6675 thermocouple design, the MAX31855 and MAX31856 are the like-for-interface successors.
What is the equivalent or alternative to the MAX6675?
There is no exact equivalent; the ADI-named alternatives are the MAX31855 and MAX31856. Each is a suggested candidate to validate in your own design, not a guaranteed drop-in, because each changes the supply rail, the output resolution or the SPI read format versus the MAX6675.
Sources // Public, primary
Sources
- Analog Devices KB KA-06721, "Best alternative to obsolete part MAX6675?" (obsolete status + named replacements)
- EngineerZone mirror of the MAX6675 alternative question
- Analog Devices MAX6675 product page (lifecycle status field)
- Analog Devices MAX6675 datasheet (PDF)
- Analog Devices MAX31855 datasheet (PDF)
- Analog Devices MAX31856 datasheet (PDF)
- Adafruit MAX31855 breakout (sold as the MAX6675 upgrade)
- Adafruit thermocouple learn guide (MAX6675 to MAX31855 migration note)
- Adafruit forums: "Difference between MAX31856, MAX31855 and MAX6675"
- Arduino forum: "Max6675 versus Max31855"
- GitHub RobTillaart/MAX6675 issue 5: distinguishing a MAX6675 and a MAX31855
Part of // Featured in
Related reading
Editorially independent and from public sources only; lifecycle, package, electrical and interface data is vendor-reported, not independently audited. Alternates are candidates to validate in your own design, confirm every detail with the manufacturer before committing.
About the author
Editorially independent and from public sources only; lifecycle, pin and rating data is vendor-reported, not independently audited. Alternates are candidates to validate in your own design. Confirm every detail with the manufacturer before committing.