MCP9808 — High-Accuracy Digital Temperature Sensor (±0.25°C Accuracy)

Overview

The MCP9808 is a high-accuracy digital temperature sensor manufactured by Microchip Technology. Operating across a wide supply range of $2.7\text{V}$ to $5.5\text{V}$ DC, it converts temperature to a 16-bit digital word over an $I^2C$ bus.

Featuring a typical accuracy of $\pm 0.25^\circ\text{C}$ from $-40^\circ\text{C}$ to $+125^\circ\text{C}$ ( $\pm 0.5^\circ\text{C}$ guaranteed maximum), the MCP9808 offers four user-selectable measurement resolutions ( $0.5^\circ\text{C}, 0.25^\circ\text{C}, 0.125^\circ\text{C}$ , and $0.0625^\circ\text{C}$ default). It includes programmable upper, lower, and critical temperature limit registers with an active hardware ALERT output pin.

Quick reference


Operating voltage (`VDD`)	2.7 V to 5.5 V DC (3.3 V or 5.0 V nominal)
Interface	$I^2C$ / SMBus (up to 400 kHz)
Default $I^2C$ address	`0x18` (`A0`, `A1`, `A2` tied to GND)
Configurable addresses	8 distinct addresses (`0x18` through `0x1F` via 3 address pins)
Typical accuracy ( $-40^\circ\text{C}$ to $+125^\circ\text{C}$ )	$\pm 0.25^\circ\text{C}$ typical / $\pm 0.5^\circ\text{C}$ max
Default resolution	16-bit ( $0.0625^\circ\text{C}$ per LSB / $1/16^\circ\text{C}$ )
Conversion time	250 ms at $0.0625^\circ\text{C}$ resolution / 30 ms at $0.5^\circ\text{C}$ resolution
Operating current	$200\ \mu\text{A}$ active / $0.1\ \mu\text{A}$ shutdown mode

Pinout (8-Pin MSOP Package & Breakout Header)

text

             ┌───┴───┐
          VDD ─┤ 1    8├─ GND
          SCL ─┤ 2    7├─ A0
          SDA ─┤ 3    6├─ A1
        ALERT ─┤ 4    5├─ A2
             └───────┘

Pin	Name	Type	Description
1	`VDD`	Power	Supply power input (+2.7 V to +5.5 V DC)
2	`SCL`	Digital Input	$I^2C$ Serial Clock
3	`SDA`	Digital Input / Output	$I^2C$ Serial Data
4	`ALERT`	Digital Output	Programmable temperature alert output pin (Open-drain)
5	`A2`	Digital Input	$I^2C$ Address Bit 2 (Default GND)
6	`A1`	Digital Input	$I^2C$ Address Bit 1 (Default GND)
7	`A0`	Digital Input	$I^2C$ Address Bit 0 (Default GND)
8	`GND`	Power	Ground reference (0 V)

Specifications

Parameter	Symbol	Min	Typ	Max	Unit	Conditions
Supply Voltage	$V_{DD}$	2.7	3.3 / 5.0	5.5	V	DC
Active Supply Current	$I_{DD}$	—	200	400	µA	Active sampling state
Shutdown Current	$I_{sd}$	—	0.1	2.0	µA	Software shutdown mode
Accuracy ( $-20^\circ\text{C} \dots +100^\circ\text{C}$ )	$T_{acc1}$	-0.5	$\pm 0.25$	+0.5	°C	Max error bound
Accuracy ( $-40^\circ\text{C} \dots +125^\circ\text{C}$ )	$T_{acc2}$	-1.0	$\pm 0.5$	+1.0	°C	Full operational spectrum
LSB Resolution ( $Mode = 3$ )	$Res_3$	—	0.0625	—	°C	16-bit 2's complement

Data Format & Celsius Math

The ambient temperature register (0x05) returns a 16-bit word formatted as follows:

Bit 15–13: Flag bits (Sign, T_CRIT, T_UPPER, T_LOWER).
Bit 12: Sign bit ( $0 = \text{Positive}, 1 = \text{Negative}$ ).
Bits 11–0: 12-bit temperature value in $0.0625^\circ\text{C}$ steps.

Positive Temperature Calculation

$\text{Temperature } (^\circ\text{C}) = \frac{\text{Raw Register Value } \& \text{ 0x1FFF}}{16.0}$

Negative Temperature Calculation (Sign Bit 12 = 1)

$\text{Temperature } (^\circ\text{C}) = 256.0 - \frac{\text{Raw Register Value } \& \text{ 0x1FFF}}{16.0}$

Wiring

MCP9808 Pin	Arduino / MCU	ESP32	Notes
`VDD`	5V / 3.3V	3.3V	Power rail
`GND`	GND	GND	System ground
`SCL`	A5	GPIO 22	$I^2C$ Clock
`SDA`	A4	GPIO 21	$I^2C$ Data

Example (Adafruit_MCP9808 Library)

cpp

#include <Wire.h>
#include "Adafruit_MCP9808.h"

Adafruit_MCP9808 tempsensor = Adafruit_MCP9808();

void setup() {
  Serial.begin(115200);
  while (!Serial) delay(10);

  Serial.println("MCP9808 High-Accuracy Temperature Sensor Test");

  // Default address 0x18
  if (!tempsensor.begin(0x18)) {
    Serial.println("MCP9808 not found! Check I2C wiring.");
    while (1);
  }

  // Set resolution to Mode 3 (0.0625°C resolution, 250ms conversion)
  tempsensor.setResolution(3);
  Serial.println("MCP9808 initialized.");
}

void loop() {
  tempsensor.wake(); // Wake up sensor

  float c = tempsensor.readTempC();
  float f = c * 9.0 / 5.0 + 32.0;

  Serial.print("Temperature: "); Serial.print(c, 4); Serial.print(" °C | ");
  Serial.print(f, 4); Serial.println(" °F");

  tempsensor.shutdown_modes(1); // Sleep to save power
  delay(2000);
}

Common mistakes

Leaving A0, A1, A2 floating: On standalone IC breakout boards, address pins A0, A1, A2 must be pulled to GND or VDD. Floating address pins cause $I^2C$ address changes between 0x18 and 0x1F.
PCB thermal conduction: Mount the sensor away from warm power supplies to avoid measuring PCB heat instead of ambient air.

Notes

MCP9808 vs TMP117 vs DS18B20: MCP9808 provides $\pm 0.25^\circ\text{C}$ accuracy over $I^2C$ ; TMP117 provides $\pm 0.1^\circ\text{C}$ medical-grade accuracy; DS18B20 provides $\pm 0.5^\circ\text{C}$ over 1-Wire.

Interface	I2C, SMBus
Supply	2.7–5.5 V
Package	8-pin MSOP / DFN / Breakout Module