component

MAX31855 Thermocouple Converter

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by adom

Cold-junction compensated thermocouple-to-digital converter with 14-bit SPI output.

thermocoupletemperaturespicold-junctionadisoic-8
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README

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MAX31855

Analog Devices · Thermocouple Interface · SOIC-8

The MAX31855 is a thermocouple-to-digital converter that digitizes a thermocouple with cold-junction compensation and a 14-bit, 0.25 C resolution result over a read-only SPI interface. It detects open, short-to-GND, and short-to-VCC faults. This page shows the K-type (MAX31855K); the family also covers J, N, T, S, R, and E types.

Pinout

Pin Name Type Function
1 GND power_in Ground reference. Connect to system ground; a large ground plane improves temperature-measurement accuracy.
2 T- input Negative thermocouple input (see Table 1 for wire type per part suffix). Do NOT connect to GND. Recommend a 10nF differential capacitor across T+/T- for noise filtering.
3 T+ input Positive thermocouple input (see Table 1 for wire type per part suffix). Bias current -100nA to +100nA at 100mV across inputs.
4 VCC power_in Power-supply voltage input, 3.0V to 3.6V (3.3V typical). Bypass to GND with a 0.1µF ceramic capacitor placed close to the pin. ICC ≈ 900µA typical, 1500µA max.
5 SCK input SPI serial-clock input, up to 5MHz. Minimum high/low pulse width 100ns; rise/fall ≤ 200ns.
6 CS input Active-low chip-select input. Drive CS low to enable the serial interface and clock out 32 bits of thermocouple + reference-junction data on SO.
7 SO output SPI serial-data output (MISO). Read-only 32-bit frame containing 14-bit thermocouple temperature, fault bit, 12-bit internal cold-junction temperature, and SCV/SCG/OC fault bits. VOH ≥ VCC-0.4V at IOUT=-1.6mA; VOL ≤ 0.4V at IOUT=1.6mA.
8 DNC unconnected Do Not Connect. Leave floating.

Key specifications

Parameter Value
Type Thermocouple-to-digital converter
Thermocouple (this variant) K-type (family: J/N/T/S/R/E/K)
Resolution 14-bit, 0.25 C
Temperature range -270 C to +1800 C (type dependent)
Cold-junction compensation Internal
Interface SPI (read-only)
Fault detection Open, short-to-GND, short-to-VCC
Supply voltage 3.0 V to 3.6 V

Ordering variants

Same part, different packaging or reel option.

  • MAX31855KASA+
  • MAX31855KASA+T
  • MAX31855JASA+
  • MAX31855JASA+T
  • MAX31855NASA+
  • MAX31855NASA+T
  • MAX31855SASA+
  • MAX31855SASA+T
  • MAX31855TASA+
  • MAX31855TASA+T
  • MAX31855EASA+
  • MAX31855EASA+T
  • MAX31855RASA+
  • MAX31855RASA+T

CAD (KiCad official)

  • Symbol: max31855.kicad_sym
  • Footprint: max31855.kicad_mod
  • 3D model: SOIC-8 body from KiCad Package_SO/SOIC-8_3.9x4.9mm_P1.27mm.

Provenance

Data extracted from the manufacturer datasheet, not a distributor listing:

  • Datasheet: Analog Devices datasheet (13 pp, sha256 0da8c21e66d26950, retrieved 2026-08-17, tier: manufacturer)
  • Extractor: ds2sf (Claude). Every pin and dimension is cited to a datasheet page; it refuses to fabricate.
  • CAD: KiCad official libraries (CC-BY-SA 4.0).

Datasheet PDF