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BME280 Environmental Sensor : Technical Specification

The BME280 is a precision digital environmental sensor combining relative humidity, barometric pressure, and ambient temperature sensing capabilities in an 8-pin metal-lid Land Grid Array (LGA) package (2.5 mm × 2.5 mm × 0.93 mm). It communicates over standard I2C and SPI digital interfaces with low power consumption for battery-constrained mobile and IoT devices.

1. Key Features & Operating Ranges

  • Sensing Parameters: Relative humidity, barometric pressure, and ambient temperature.
  • Supply Voltage:
    • Main analog supply (VDD): 1.71 V to 3.6 V.
    • Digital interface supply (VDDIO): 1.2 V to 3.6 V.
  • Low Current Consumption:
    • 0.1 µA in Sleep mode.
    • 1.8 µA @ 1 Hz (Humidity + Temperature).
    • 3.6 µA @ 1 Hz (Humidity + Pressure + Temperature).
  • Operating Range: -40 °C to +85 °C, 0% to 100% relative humidity, 300 hPa to 1100 hPa.
  • Digital Interfaces: I2C (up to 3.4 MHz) and SPI (3-wire and 4-wire, up to 10 MHz).

2. Pin Configuration

Pin # Name Type Description
1 GND Supply Ground connection.
2 CSB Digital Input Chip Select (active low). Connect to VDDIO for I2C mode.
3 SDI Digital I/O Serial Data Input. Functions as SDA in I2C mode and MOSI in SPI mode.
4 SCK Digital Input Serial Clock. Functions as SCL in I2C mode and SCK in SPI mode.
5 SDO Digital Output Serial Data Output (MISO in SPI mode). Sets bit 0 of the I2C slave address.
6 VDDIO Supply Digital interface power supply (1.2 V to 3.6 V).
7 GND Supply Ground connection.
8 VDD Supply Main analog power supply (1.71 V to 3.6 V).

3. Absolute Maximum Ratings

Caution: Exceeding any parameter in Table 2 can cause permanent silicon damage. Extended exposure to absolute maximum rating conditions can degrade overall device reliability.

Table 2: Absolute Maximum Ratings

Parameter Condition Min Max Unit
Supply Voltage (VDD, VDDIO) Voltage at any supply pin -0.3 4.25 V
Interface Pin Voltage Voltage at SDI, SDO, SCK, CSB -0.3 VDDIO + 0.3 V
Storage Temperature ≤ 65% Relative Humidity -45 +85 °C
Overpressure Tolerance Static pressure 0 20,000 hPa
ESD (Human Body Model) HBM, all pins — ±2 kV
ESD (Charge Device Model) CDM — ±500 V
ESD (Machine Model) MM — ±200 V

4. Digital Interfaces

The BME280 operates as a slave device on both I2C and SPI digital buses. The active interface is selected automatically depending on the logic state of the CSB pin at startup:

  • I2C mode: Connect `CSB` directly to the `VDDIO` rail.
  • SPI mode: Drive `CSB` low to initialize SPI communication. Once pulled low, the device remains locked in SPI mode until the next Power-On Reset (POR).

4.1 I2C Interface

The I2C interface complies with the Philips I2C Specification version 2.1 and supports Standard Mode, Fast Mode, and High-Speed (HS) mode (up to 3.4 MHz).

  • Bus Lines:
    • `SCK` acts as serial clock line (`SCL`).
    • `SDI` acts as serial data line (`SDA`) and requires an external pull-up resistor (typically 4.7 kΩ) to `VDDIO`.
  • Slave Addressing: The 7-bit device address is defined by the hardware logic level of the `SDO` pin:
    • `SDO` tied to `GND`: 0x76 (1110110b)
    • `SDO` tied to `VDDIO`: 0x77 (1110111b)

Important: Never leave the SDO pin floating, as this results in an undefined I2C bus address.

  • Burst Read Operation: Always read measurement registers (0xF7 through 0xFE) in a continuous multi-byte burst read transaction. Individual byte reads can cause race conditions where sensor data updates mid-read, resulting in inconsistent telemetry.

4.2 SPI Interface

The sensor supports both SPI Mode 00 (CPOL = 0, CPHA = 0) and SPI Mode 11 (CPOL = 1, CPHA = 1) with clock frequencies up to 10 MHz.

  • 4-Wire SPI (Default):
    • `CSB`: Chip Select (active low).
    • `SCK`: Serial Clock.
    • `SDI`: Serial Data Input / MOSI (latched on the rising edge of `SCK`).
    • `SDO`: Serial Data Output / MISO (shifted out on the falling edge of `SCK`).
  • 3-Wire SPI: Set the spi3w_en bit to 1 in the config register (0xF5, bit 0) to enable bidirectional data transfer on `SDI`. In this configuration, `SDO` remains in a high-impedance (high-Z) state.
  • SPI Addressing Convention: Bit 7 of the 8-bit SPI transaction header controls read/write access (0 for Write, 1 for Read), followed by the 7-bit target register address.