BQ25756E Multiplatform Library

A C++ library for controlling the BQ25756E buck-boost battery charge controller from Texas Instruments via I2C. Supports Arduino, ESP32, and STM32 platforms with compile-time platform detection.

Features

• Multi-platform: Single codebase for Arduino/ESP32 (Wire) and STM32 (HAL)
• Charge control: Configurable voltage, current, pre-charge, and termination limits
• Safety timers: Watchdog, top-off, charge safety, and constant-voltage timers
• ADC monitoring: Input/battery voltage and current, temperature sensor, feedback voltage
• MPPT support: Maximum Power Point Tracking for solar panel applications
• Fault protection: Over-voltage, over-current, thermal shutdown detection
• Reverse mode: Bidirectional power path with configurable discharge current

Architecture

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

Loading

include/
├── bq25756e.h                 # Driver class, registers, bit masks, config struct
├── bq25756e_platform_config.h # Compile-time platform detection
└── bq25756e_platform_i2c.h    # Platform-agnostic I2C function declarations
src/
├── bq25756e.cpp               # Driver implementation
└── bq25756e_platform_i2c.cpp  # Arduino (Wire) and STM32 (HAL) I2C implementations

Installation

PlatformIO

Add to your platformio.ini:

lib_deps =
    https://github.com/theohg/bq25756e_multiplatform.git#v1.0.0

Arduino IDE

1. Download or clone this repository
2. Copy into your Arduino libraries/ folder
3. Restart the Arduino IDE

STM32 (CubeMX / HAL)

1. Copy include/ and src/ into your project
2. The HAL header is auto-detected from your STM32 family define (e.g. STM32F4xx). If auto-detection fails, add -DBQ25756E_STM32_HAL_HEADER='"stm32f4xx_hal.h"' to your build flags
3. Call bq25756e_i2c_set_handle(&hi2c1) once in your initialization code before using the driver

Quick Start

Arduino / ESP32

#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(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;  // mV (FB voltage)
    cfg.chargeCurrentLimit      = 2000;  // mA
    cfg.inputCurrentDPMLimit    = 3000;  // mA
    cfg.inputVoltageDPMLimit    = 4200;  // mV
    cfg.prechargeCurrentLimit   = 500;   // mA
    cfg.terminationCurrentLimit = 250;   // mA
    cfg.terminationControlEnabled = true;
    cfg.fastChargeThreshold     = 0b10;  // 66.7% x VFB_REG
    cfg.prechargeControlEnabled = true;
    cfg.chargeEnabled           = true;
    cfg.verbose                 = true;
    charger.init(cfg);
}

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

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

    delay(2000);
}

STM32

// In main.c, after MX_I2C1_Init():
#include "bq25756e.h"

bq25756e_i2c_set_handle(&hi2c1);  // Required before any BQ25756E operation

BQ25756E charger(0x6A, 500, 5000, 5000, 4200, 36000);
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;
charger.init(cfg);

See the examples/ folder for complete, compilable examples.

API Overview

Charge Control

Method	Description
init(cfg)	Initialize charger with configuration struct
setChargeVoltageLimit(mV)	Set 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 all registers to defaults

Configuration

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

Status & ADC

Method	Returns
getChargeCycleStatus()	Charge cycle state (0-7)
getChargerStatus1/2/3()	Status register bytes
getFaultStatus()	Fault flags (OV, OC, TSHUT, etc.)
getVBATADC()	Battery voltage [mV]
getVACADC()	Input voltage [mV]
getIBATADC()	Battery current [mA]
getIACADC()	Input current [mA]
getTSADC()	TS pin reading [% of REGN]
getVFBADC()	Feedback voltage [mV]
getPartInformation()	Part number and revision

Debug

Method	Description
setDebugStream(&Serial)	Set debug output stream (Arduino only)
printChargerConfig()	Print all register values

License

MIT License -- see LICENSE.txt for details.

Copyright (c) 2026 Theo Heng