BQ27441 Rust Driver

A no_std Rust driver for the Texas Instruments BQ27441-G1 battery fuel gauge IC.

Features

• I²C Communication: Full support for blocking and async I²C operations
• Comprehensive Battery Monitoring:
  • State of Charge (SOC) - 0-100%
  • Voltage measurements (mV)
  • Current measurements (mA)
  • Temperature readings (°C or 0.1K)
  • Remaining capacity (mAh)
  • Full charge capacity (mAh)
  • State of Health (SOH) percentage
  • Average power (mW)
• Power Management: Support for NORMAL, SLEEP, HIBERNATE, and SHUTDOWN modes
• Configuration: Data Memory access for customization
• Security: SEALED/UNSEALED modes
• YAML-Based Register Definitions: Uses device-driver crate for type-safe register access
• Async Support: Optional async/await support via embedded-hal-async
• Embassy Compatible: Works seamlessly with the Embassy framework
• defmt Support: Optional defmt logging for debugging

Hardware

The BQ27441-G1 is a System-Side Impedance Track™ Fuel Gauge for single-cell Li-Ion batteries.

• I²C Address: 0x55 (default)
• Supply Voltage: 1.8V - 3.6V
• Sense Resistor: Typically 10mΩ between SRN and SRP pins
• Variants:
  • BQ27441-G1A: For 4.2V maximum charge voltage batteries
  • BQ27441-G1B: For 4.3V or 4.35V maximum charge voltage batteries

Usage

Blocking I²C

use bq27441::Bq27441;
use embedded_hal::i2c::I2c;

// Create driver with default I2C address (0x55)
let mut gauge = Bq27441::new(i2c)?;

// Read battery status
let voltage = gauge.voltage()?;              // mV
let soc = gauge.state_of_charge()?;          // %
let capacity = gauge.remaining_capacity()?;  // mAh
let current = gauge.average_current()?;      // mA (signed)
let temp = gauge.temperature_celsius()?;     // °C

// Check charging status
if gauge.is_charging()? {
    println!("Battery is charging");
}

if gauge.is_full_charged()? {
    println!("Battery is fully charged");
}

Async I²C (with Embassy)

use bq27441::Bq27441Async;
use embedded_hal_async::i2c::I2c;

// Create async driver
let mut gauge = Bq27441Async::new(i2c).await?;

// Read battery status asynchronously
let voltage = gauge.voltage().await?;
let soc = gauge.state_of_charge().await?;
let capacity = gauge.remaining_capacity().await?;

Advanced Configuration

// Unseal device for configuration
gauge.unseal()?;

// Enter config update mode
gauge.enter_config_mode()?;

// Modify configuration via Data Memory
// (See datasheet for details)

// Exit config mode
gauge.exit_config_mode()?;

// Seal device to protect configuration
gauge.seal()?;

Examples

See the examples/ directory for complete working examples:

• stm32wba65ri_embassy.rs - Embassy async example for STM32WBA65RI

To run an example:

cargo build --example stm32wba65ri_embassy --features embassy --target thumbv8m.main-none-eabihf

API Overview

Core Methods

• voltage() - Read battery voltage in mV
• state_of_charge() - Read SOC percentage (0-100%)
• remaining_capacity() - Read remaining capacity in mAh
• full_charge_capacity() - Read full charge capacity in mAh
• average_current() - Read average current in mA (signed)
• average_power() - Read average power in mW (signed)
• temperature_celsius() - Read temperature in °C
• state_of_health() - Read SOH percentage

Status Methods

• is_battery_detected() - Check if battery is connected
• is_charging() - Check if battery is charging
• is_discharging() - Check if battery is discharging
• is_full_charged() - Check if battery is fully charged
• flags() - Read all status flags

Control Methods

• control_read(cmd) - Send control subcommand and read response
• control_write(cmd) - Send control subcommand
• firmware_version() - Read firmware version
• chemistry_id() - Read chemistry ID
• seal() - Enter SEALED mode
• unseal() - Exit SEALED mode
• enter_config_mode() - Enter CONFIG UPDATE mode
• exit_config_mode() - Exit CONFIG UPDATE mode
• set_hibernate() / clear_hibernate() - Hibernate mode control

Features

Enable optional features in your Cargo.toml:

[dependencies]
bq27441 = { version = "0.1", features = ["async", "defmt-03"] }

Available features:

• async - Enable async/await support
• defmt-03 - Enable defmt logging
• embassy - Enable both async and defmt (convenience feature)

Register Access

For low-level register access, use the .device() method:

// Access generated device API directly
let flags = gauge.device().flags().read()?;
if flags.bat_det() {
    println!("Battery detected");
}

Development

Building

# Build for embedded target
cargo build --target thumbv8m.main-none-eabihf

# Build with async support
cargo build --target thumbv8m.main-none-eabihf --features async

# Build with Embassy + defmt
cargo build --target thumbv8m.main-none-eabihf --features embassy

Register Definitions

Register definitions are maintained in src/bq27441.yaml using the device-driver crate's YAML format. The build script (build.rs) generates type-safe register access code at compile time.

License

Licensed under either of:

• Apache License, Version 2.0 (LICENSE-APACHE or http://www.apache.org/licenses/LICENSE-2.0)
• MIT license (LICENSE-MIT or http://opensource.org/licenses/MIT)

at your option.

References

• BQ27441-G1 Datasheet
• BQ27441-G1 Technical Reference
• device-driver crate
• Embassy framework