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MAX31865 RTD-to-Digital Converter

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by Ray

Resistance-to-digital converter for PT100/PT1000 RTD temperature sensors, SPI.

rtdpt100pt1000temperaturespiaditssop-20
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MAX31865

Analog Devices · RTD Interface · TSSOP-20

The MAX31865 is a resistance-to-digital converter optimized for platinum RTDs (PT100 and PT1000). It digitizes the RTD resistance with a 15-bit ADC and reports it over SPI, handling the reference-resistor ratiometric measurement, 2/3/4-wire configurations, and fault detection (open, short, overvoltage). It gives precise, low-drift temperature measurement for industrial sensing.

Pinout

Pin Name Type Function
1 DRDY output Active-low, push-pull data-ready output. DRDY goes low when a new conversion result is available in the RTD data register; it returns high after that register is read.
2 DVDD power_in Digital supply voltage input, 3.0V-3.6V (nominally 3.3V). Bypass to DGND with a 0.1µF capacitor.
3 VDD power_in Analog supply voltage input, 3.0V-3.6V (nominally 3.3V). Bypass to GND1 with a 0.1µF capacitor.
4 BIAS output Bias voltage output (VBIAS ≈ 2.0V). Provides the bias for the reference and RTD networks; drives up to 5.75mA.
5 REFIN+ input Positive reference-voltage input. Connect to BIAS. Reference resistor (RREF, 350Ω-10kΩ) is placed between REFIN+ and REFIN-.
6 REFIN- input Negative reference-voltage input. Reference resistor is connected between REFIN+ and REFIN-.
7 ISENSOR passive Low side of RREF; connect to REFIN-. Carries the RTD bias current returning through the reference resistor.
8 FORCE+ output High-side RTD drive. Connect to FORCE2 when using the 3-wire connection configuration. Protected to ±45V.
9 FORCE2 bidirectional Positive input used in 3-wire configuration only. Tie to FORCE+ for 3-wire RTDs; ground for 2-wire and 4-wire configurations. Protected to ±45V.
10 RTDIN+ input Positive RTD sense input. Protected to ±45V.
11 RTDIN- input Negative RTD sense input. Protected to ±45V.
12 FORCE- passive Low-side RTD return. Protected to ±45V.
13 GND2 power_in Analog ground. Connect to GND1.
14 SDI input SPI serial-data input (MOSI). Sampled on the rising edge of SCLK.
15 SCLK input SPI serial-data clock input.
16 CS input Active-low chip select. Drive CS low to enable the SPI interface.
17 SDO output SPI serial-data output (MISO).
18 DGND power_in Digital ground.
19 GND1 power_in Analog ground. Connect to GND2.
20 N.C. unconnected No internal connection. Do not connect.

Key specifications

Parameter Value
Type RTD-to-digital converter
Sensors PT100 / PT1000 (2/3/4-wire)
ADC 15-bit
Accuracy 0.5% of full scale (max)
Interface SPI
Fault detection Open, short, overvoltage
Supply voltage 3.0 V to 3.6 V
Operating temperature -40 C to 85 C

Ordering variants

Same part, different packaging or reel option.

  • MAX31865AAP+
  • MAX31865AAP+T
  • MAX31865ATP+
  • MAX31865ATP+T

CAD (KiCad official)

  • Symbol: max31865.kicad_sym
  • Footprint: max31865.kicad_mod
  • 3D model: TSSOP-20 body from KiCad Package_SO/TSSOP-20_4.4x6.5mm_P0.65mm.

Provenance

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

  • Datasheet: Analog Devices datasheet (26 pp, sha256 88f540410eb8c2ac, 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