Original question:
Tool/software:
Hello,
I have 5 cells in series using bq7791500 BMS I have tested separately that part with 2 A charging current and it works fine.
After connecting the charger i cant get more than 0.9A of charging current.
Input voltage 24V
Battery pack discharged to 18V
/* USER CODE BEGIN Header */
/**
******************************************************************************
* @file : main.c
* @brief : Main program body
******************************************************************************
* @attention
*
* Copyright (c) 2025 STMicroelectronics.
* All rights reserved.
*
* This software is licensed under terms that can be found in the LICENSE file
* in the root directory of this software component.
* If no LICENSE file comes with this software, it is provided AS-IS.
*
******************************************************************************
*/
/* USER CODE END Header */
/* Includes ------------------------------------------------------------------*/
#include "main.h"
/* Private includes ----------------------------------------------------------*/
/* USER CODE BEGIN Includes */
#include <stdio.h>
/* USER CODE END Includes */
/* Private typedef -----------------------------------------------------------*/
/* USER CODE BEGIN PTD */
/* USER CODE END PTD */
/* Private define ------------------------------------------------------------*/
/* USER CODE BEGIN PD */
//extern I2C_HandleTypeDef hi2c1;
#define BQ25756E_I2C_ADDRESS (0x6A << 1) // 7-bit address 0x6B, shifted for 8-bit R/W byte
//extern I2C_HandleTypeDef hi2c1; // Assuming I2C1 is used
I2C_HandleTypeDef hi2c1;
/* USER CODE END PD */
/* Private macro -------------------------------------------------------------*/
/* USER CODE BEGIN PM */
/* USER CODE END PM */
/* Private variables ---------------------------------------------------------*/
const uint8_t bq25756e_register_map[] = {
0x00, // REG0x00_Charge_Voltage_Limit
0x02, // REG0x02_Charge_Current_Limit
0x04, // REG0x04_Input_Current_DPM_Limit
0x06, // REG0x06_Input_Voltage_DPM_Limit
0x0A, // REG0x0A_Reverse_Mode_Input_Current_Limit
0x0C, // REG0x0C_Reverse_Mode_Input_Voltage_Limit
0x10, // REG0x10_Precharge_Current_Limit
0x12, // REG0x12_Termination_Current_Limit
0x14, // REG0x14_Precharge_and_Termination_Control
0x15, // REG0x15_Timer_Control
0x16, // REG0x16_Three-Stage_Charge_Control
0x17, // REG0x17_Charger_Control
0x18, // REG0x18_Pin_Control
0x19, // REG0x19_Power_Path_and_Reverse_Mode_Control
0x1A, // REG0x1A_MPPT_Control
0x1B, // REG0x1B_TS_Charging_Threshold_Control
0x1C, // REG0x1C_TS_Charging_Region_Behavior_Control
0x1D, // REG0x1D_TS_Reverse_Mode_Threshold_Control
0x1E, // REG0x1E_Reverse_Undervoltage_Control
0x1F, // REG0x1F_VAC_Max_Power_Point_Detect
0x21, // REG0x21_Charger_Status_1
0x22, // REG0x22_Charger_Status_2
0x23, // REG0x23_Charger_Status_3
0x24, // REG0x24_Fault_Status
0x25, // REG0x25_Charger_Flag_1
0x26, // REG0x26_Charger_Flag_2
0x27, // REG0x27_Fault_Flag
0x28, // REG0x28_Charger_Mask_1
0x29, // REG0x29_Charger_Mask_2
0x2A, // REG0x2A_Fault_Mask
0x2B, // REG0x2B_ADC_Control
0x2C, // REG0x2C_ADC_Channel_Control
0x2D, // REG0x2D_ADC_Data
0x2E, // REG0x2E_IBAT_ADC
0x2F, // REG0x2F_IBAT_ADC (duplicate in image, assuming typo or 16-bit register, reading as 16-bit)
0x31, // REG0x31_VAC_ADC
0x37, // REG0x37_VBAT_ADC
0x38, // REG0x38_TS_ADC
0x39, // REG0x39_VFB_ADC
0x3B, // REG0x3B_Gate_Driver_Strength_Control
0x3C, // REG0x3C_Gate_Driver_Dead_Time_Control
0x3D, // REG0x3D_Part_Information
0x62 // REG0x62_Reverse_Mode_Battery_Discharge_Current
};
#define NUM_BQ25756E_REGISTERS (sizeof(bq25756e_register_map) / sizeof(bq25756e_register_map[0]))
uint16_t bq25756e_registers[NUM_BQ25756E_REGISTERS];
/* USER CODE BEGIN PV */
/* USER CODE END PV */
/* Private function prototypes -----------------------------------------------*/
void SystemClock_Config(void);
static void MX_GPIO_Init(void);
static void MX_I2C1_Init(void);
/* USER CODE BEGIN PFP */
void BQ25756E_ReadAllRegisters(void) {
uint8_t reg_addr;
uint8_t read_buffer[2]; // Buffer to store the two bytes read (high byte, low byte)
for (int i = 0; i < NUM_BQ25756E_REGISTERS; i++) {
reg_addr = bq25756e_register_map[i];
// I2C Single Read Sequence (as per Figure 8-12 in your diagram):
// S | Target Addr (W) | ACK | Reg Addr | ACK | S | Target Addr (R) | ACK | Data (High Byte) | ACK | Data (Low Byte) | NCK | P
// 1. Transmit Register Address (Write phase)
// This sends the START condition, Slave Address (Write), and the Register Address.
// HAL_I2C_Master_Transmit returns HAL_OK on success.
if (HAL_I2C_Master_Transmit(&hi2c1, BQ25756E_I2C_ADDRESS, ®_addr, 1, HAL_MAX_DELAY) != HAL_OK) {
// Error handling: If transmission fails, skip to the next register.
// In a real application, you might want more robust error reporting.
continue;
}
// 2. Receive Data (Read phase)
// This implicitly handles the Repeated START condition, Slave Address (Read),
// and then reads the specified number of bytes.
// The BQ25756E registers are 16-bit, so we read 2 bytes.
// HAL_I2C_Master_Receive returns HAL_OK on success.
if (HAL_I2C_Master_Receive(&hi2c1, BQ25756E_I2C_ADDRESS, read_buffer, 2, HAL_MAX_DELAY) != HAL_OK) {
// Error handling: If reception fails, skip to the next register.
continue;
}
// Store the 16-bit value. The BQ25756E typically sends MSB (Most Significant Byte) first.
// So, read_buffer[0] is the high byte, and read_buffer[1] is the low byte.
bq25756e_registers[i] = (uint16_t)((read_buffer[0] << 8) | read_buffer[1]);
}
}
/* USER CODE END PFP */
/* Private user code ---------------------------------------------------------*/
/* USER CODE BEGIN 0 */
/* USER CODE END 0 */
/**
* @brief The application entry point.
* @retval int
*/
int main(void)
{
/* USER CODE BEGIN 1 */
// Optional: Init UART for printf
// MX_USART2_UART_Init();
/* USER CODE END 1 */
/* MCU Configuration--------------------------------------------------------*/
/* Reset of all peripherals, Initializes the Flash interface and the Systick. */
HAL_Init();
/* USER CODE BEGIN Init */
/* USER CODE END Init */
/* Configure the system clock */
SystemClock_Config();
/* USER CODE BEGIN SysInit */
/* USER CODE END SysInit */
/* Initialize all configured peripherals */
MX_GPIO_Init();
MX_I2C1_Init();
/* USER CODE BEGIN 2 */
BQ25756E_ReadAllRegisters();
/* USER CODE END 2 */
/* Infinite loop */
/* USER CODE BEGIN WHILE */
while (1)
{
/* USER CODE END WHILE */
/* USER CODE BEGIN 3 */
}
/* USER CODE END 3 */
}
/**
* @brief System Clock Configuration
* @retval None
*/
void SystemClock_Config(void)
{
RCC_OscInitTypeDef RCC_OscInitStruct = {0};
RCC_ClkInitTypeDef RCC_ClkInitStruct = {0};
/** Configure the main internal regulator output voltage
*/
__HAL_PWR_VOLTAGESCALING_CONFIG(PWR_REGULATOR_VOLTAGE_SCALE1);
/** Initializes the RCC Oscillators according to the specified parameters
* in the RCC_OscInitTypeDef structure.
*/
RCC_OscInitStruct.OscillatorType = RCC_OSCILLATORTYPE_HSI;
RCC_OscInitStruct.HSIState = RCC_HSI_ON;
RCC_OscInitStruct.HSICalibrationValue = RCC_HSICALIBRATION_DEFAULT;
RCC_OscInitStruct.PLL.PLLState = RCC_PLL_ON;
RCC_OscInitStruct.PLL.PLLSource = RCC_PLLSOURCE_HSI;
RCC_OscInitStruct.PLL.PLLMUL = RCC_PLL_MUL6;
RCC_OscInitStruct.PLL.PLLDIV = RCC_PLL_DIV3;
if (HAL_RCC_OscConfig(&RCC_OscInitStruct) != HAL_OK)
{
Error_Handler();
}
/** Initializes the CPU, AHB and APB buses clocks
*/
RCC_ClkInitStruct.ClockType = RCC_CLOCKTYPE_HCLK|RCC_CLOCKTYPE_SYSCLK
|RCC_CLOCKTYPE_PCLK1|RCC_CLOCKTYPE_PCLK2;
RCC_ClkInitStruct.SYSCLKSource = RCC_SYSCLKSOURCE_PLLCLK;
RCC_ClkInitStruct.AHBCLKDivider = RCC_SYSCLK_DIV1;
RCC_ClkInitStruct.APB1CLKDivider = RCC_HCLK_DIV1;
RCC_ClkInitStruct.APB2CLKDivider = RCC_HCLK_DIV1;
if (HAL_RCC_ClockConfig(&RCC_ClkInitStruct, FLASH_LATENCY_1) != HAL_OK)
{
Error_Handler();
}
}
/**
* @brief I2C1 Initialization Function
* @param None
* @retval None
*/
static void MX_I2C1_Init(void)
{
/* USER CODE BEGIN I2C1_Init 0 */
/* USER CODE END I2C1_Init 0 */
/* USER CODE BEGIN I2C1_Init 1 */
/* USER CODE END I2C1_Init 1 */
hi2c1.Instance = I2C1;
hi2c1.Init.ClockSpeed = 100000;
hi2c1.Init.DutyCycle = I2C_DUTYCYCLE_2;
hi2c1.Init.OwnAddress1 = 0;
hi2c1.Init.AddressingMode = I2C_ADDRESSINGMODE_7BIT;
hi2c1.Init.DualAddressMode = I2C_DUALADDRESS_DISABLE;
hi2c1.Init.OwnAddress2 = 0;
hi2c1.Init.GeneralCallMode = I2C_GENERALCALL_DISABLE;
hi2c1.Init.NoStretchMode = I2C_NOSTRETCH_DISABLE;
if (HAL_I2C_Init(&hi2c1) != HAL_OK)
{
Error_Handler();
}
/* USER CODE BEGIN I2C1_Init 2 */
/* USER CODE END I2C1_Init 2 */
}
/**
* @brief GPIO Initialization Function
* @param None
* @retval None
*/
static void MX_GPIO_Init(void)
{
/* USER CODE BEGIN MX_GPIO_Init_1 */
/* USER CODE END MX_GPIO_Init_1 */
/* GPIO Ports Clock Enable */
__HAL_RCC_GPIOB_CLK_ENABLE();
/* USER CODE BEGIN MX_GPIO_Init_2 */
/* USER CODE END MX_GPIO_Init_2 */
}
/* USER CODE BEGIN 4 */
/* USER CODE END 4 */
/**
* @brief This function is executed in case of error occurrence.
* @retval None
*/
void Error_Handler(void)
{
/* USER CODE BEGIN Error_Handler_Debug */
/* User can add his own implementation to report the HAL error return state */
__disable_irq();
while (1)
{
}
/* USER CODE END Error_Handler_Debug */
}
#ifdef USE_FULL_ASSERT
/**
* @brief Reports the name of the source file and the source line number
* where the assert_param error has occurred.
* @param file: pointer to the source file name
* @param line: assert_param error line source number
* @retval None
*/
void assert_failed(uint8_t *file, uint32_t line)
{
/* USER CODE BEGIN 6 */
/* User can add his own implementation to report the file name and line number,
ex: printf("Wrong parameters value: file %s on line %d\r\n", file, line) */
/* USER CODE END 6 */
}
#endif /* USE_FULL_ASSERT */
SW1 - Yellow
SW2 - Blue
Output voltage - green
output current ( measured with long GND leads ) 
Input current, input voltage. I replaced the switching transistors with lower input capacitance because there was high temperature rising on the IC drivers.
measured with spring probe 
Q3 and Q4 gate drives
Input voltage is stable all the time
