BQ25756E Multiplatform Library

🔋 Featured in the EPFL Xplore Mars-rover power board — firmware (ElonMux) & hardware. This library manages its high-power battery charging.

A C++ library for controlling the BQ25756E buck-boost battery charge controller from Texas Instruments via I2C. It supports Arduino, ESP32, STM32, and RP2040 targets and uses a per-instance bus handle so multiple buses or devices can be used without global transport state.

Features

• Multi-platform: Single codebase for Arduino/ESP32 (Wire), STM32 (HAL), and RP2040
• Bus-first design: The active I2C bus is passed directly into the constructor
• Charge control: Configurable voltage, current, pre-charge, and termination limits
• Safety timers: Watchdog, top-off, charge safety, and constant-voltage timers
• ADC monitoring: Input and battery voltage/current, TS pin, and feedback voltage reads
• MPPT support: Maximum Power Point Tracking for solar-oriented applications
• Fault protection: Over-voltage, over-current, watchdog, and thermal status handling

Architecture

graph TD
        A[User Application] --> B[BQ25756E Driver Class]
        B --> C[I2C Abstraction Layer]
        C --> D{Platform?}
        D -->|Arduino / ESP32 / RP2040 Arduino core| E[Wire Library]
        D -->|STM32| F[HAL I2C]
        D -->|RP2040 Pico SDK| J[Pico SDK I2C]

        B --> G[Charge Control]
        B --> H[Configuration]
        B --> I[ADC Monitoring]

        G --> G1[setChargeVoltageLimit]
        G --> G2[setChargeCurrentLimit]
        G --> G3[enableCharge / disableCharge]

        style A fill:#e1f5fe
        style B fill:#fff3e0
        style C fill:#f3e5f5
        style E fill:#e8f5e9
        style F fill:#e8f5e9
        style J fill:#e8f5e9

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Repository Layout

include/
    bq25756e.h
    bq25756e_platform_config.h
    bq25756e_platform_i2c.h
src/
    bq25756e.cpp
    bq25756e_platform_i2c.cpp
examples/
    basic_charging/
    status_monitoring/
.github/workflows/
    ci.yml
    release.yml

Installation

PlatformIO

Add to your platformio.ini:

lib_deps =
        https://github.com/theohg/bq25756e_multiplatform.git#v1.1.0

Arduino IDE

Download the repository or a release zip, then add it through Sketch -> Include Library -> Add .ZIP Library.

STM32 HAL / Pico SDK

Copy include/ and src/ into your project, make sure the correct HAL or Pico SDK headers are available to the compiler, and keep I2C initialization in your application code.

Usage Pattern

1. Initialize the I2C peripheral yourself.
2. Pass the active bus handle as constructor argument 1: &Wire, &hi2c1, i2c0, or i2c1.
3. Pass the 7-bit device address as constructor argument 2.
4. Call init(...) before using the driver.

For Arduino-based Pico builds, use &Wire. For pure Pico SDK builds, use i2c0 or i2c1 directly.

Quick Start

Arduino / ESP32 / RP2040 Arduino core

#include <Wire.h>
#include <bq25756e.h>

#define BQ25756E_ADDR       0x6A
#define SWITCHING_FREQ      500
#define MAX_CHARGE_CURRENT  5000
#define MAX_INPUT_CURRENT   5000
#define MIN_INPUT_VOLTAGE   4200
#define MAX_INPUT_VOLTAGE   36000

BQ25756E charger(&Wire, BQ25756E_ADDR, SWITCHING_FREQ,
                                 MAX_CHARGE_CURRENT, MAX_INPUT_CURRENT,
                                 MIN_INPUT_VOLTAGE, MAX_INPUT_VOLTAGE);

void setup() {
        Serial.begin(115200);
        Wire.begin();

        charger.setDebugStream(&Serial);

        BQ25756E_Config cfg;
        cfg.chargeVoltageLimit        = 1536;
        cfg.chargeCurrentLimit        = 2000;
        cfg.inputCurrentDPMLimit      = 3000;
        cfg.inputVoltageDPMLimit      = 4200;
        cfg.prechargeCurrentLimit     = 500;
        cfg.terminationCurrentLimit   = 250;
        cfg.terminationControlEnabled = true;
        cfg.prechargeControlEnabled   = true;
        cfg.chargeEnabled             = true;
        cfg.verbose                   = true;
        charger.init(cfg);
}

void loop() {
        Serial.print("VBAT: ");
        Serial.println(charger.getVBATADC());

        Serial.print("Status: ");
        Serial.println(charger.getChargeCycleStatus());
        delay(2000);
}

STM32 HAL / Pico SDK

#include "bq25756e.h"

BQ25756E charger(&hi2c1, 0x6A, 500, 5000, 5000, 4200, 36000);
// For a pure Pico SDK project, pass i2c0 or i2c1 instead of &hi2c1.

void app_init() {
        BQ25756E_Config cfg;
        cfg.chargeVoltageLimit      = 1536;
        cfg.chargeCurrentLimit      = 2000;
        cfg.inputCurrentDPMLimit    = 3000;
        cfg.inputVoltageDPMLimit    = 4200;
        cfg.prechargeCurrentLimit   = 500;
        cfg.terminationCurrentLimit = 250;
        cfg.chargeEnabled           = true;
        charger.init(cfg);
}

Functional Overview

Charger Capabilities

Capability	Description
Charge configuration	Set charge voltage, fast-charge current, pre-charge, and termination limits
Input management	Configure input current and voltage DPM thresholds
Safety features	Control watchdog, top-off, safety timer, and constant-voltage timing
Monitoring	Read battery, input, feedback, current, and temperature-related ADC channels
Advanced control	Use MPPT and reverse-mode related settings when the application needs them

API Overview

Charge Control

Method	Description
init(cfg)	Initialize charger with a configuration struct
setChargeVoltageLimit(mV)	Set the FB voltage regulation limit
setChargeCurrentLimit(mA)	Set fast-charge current limit
setInputCurrentLimit(mA)	Set input current DPM limit
setInputVoltageDPM(mV)	Set input voltage DPM limit
enableCharge() / disableCharge()	Enable or disable charging
setReverseMode(enable)	Enable or disable reverse mode
resetRegisters()	Reset device registers to defaults

Configuration

Method	Description
setPrechargeCurrentLimit(mA)	Set pre-charge current
setTerminationCurrentLimit(mA)	Set termination current threshold
configurePrechargeTermination(...)	Configure pre-charge and termination behavior
configureTopOffTimer(timer)	Set top-off timer duration
configureWatchdogTimer(timer)	Set watchdog timer duration
configureChargeSafetyTimer(...)	Configure charge safety timer
configureADC(...)	Configure ADC mode, sampling, and averaging
setTSPinFunction(enable)	Enable or disable TS pin handling

Status and ADC

Method	Returns
getChargeCycleStatus()	Charge cycle state
getChargerStatus1() / getChargerStatus2() / getChargerStatus3()	Status register bytes
getFaultStatus()	Fault flags
getVBATADC()	Battery voltage [mV]
getVACADC()	Input voltage [mV]
getIBATADC()	Battery current [mA]
getIACADC()	Input current [mA]
getTSADC()	TS pin reading
getVFBADC()	Feedback voltage [mV]
getPartInformation()	Part number and revision

Debug

Method	Description
setDebugStream(&Serial)	Set debug output stream on Arduino-style targets
printChargerConfig()	Print register values and configuration

Examples

• examples/basic_charging/basic_charging.ino
• examples/status_monitoring/status_monitoring.ino

Notes

• Device addresses are always 7-bit.
• For Arduino-based Pico builds, use &Wire; for pure Pico SDK builds, pass i2c0 or i2c1.
• setDebugStream() is optional and mainly useful on Arduino-style targets.
• PlatformIO CI compiles the examples on Arduino Nano, ESP32, STM32, and RP2040.

You Like This Library? See Also

• DRV8214 Multiplatform
• INA228 Multiplatform
• TPS26750 Multiplatform

License

MIT License. See LICENSE.txt for details.

Copyright (c) 2026 Theo Heng