Part Number:BQ76940
Hi there. I designed a PCB based on TI reference for BQ76940. The Altium designer project is attached.
As you can see, I'm trying to host the chip with an stm32f103 microcontroller. Since I didn't find any libraries compatible with my MCU and IDE (Keil V5) I tried to rewrite the Arduino library by SparkFun. I successfully managed to connect to the chip via I2C and read the SYS_STAT register. Another thing that you should know is that I wasn't so sure of my design so I didn't want to test the board with a real LFP battery pack since they are expensive and dangerous! So I used 15 75 ohm resistors in series connected to a 27V power supply and I am planning to change the OV and UV threshold to match my "Battery simulator" and then test the board and the program. The problem I have is with the DEVICE_XREADY situation! No matter what I do, I get 0x20 as soon as the chip is booted and I can't reset the bit. The datasheet indicates that DEVICE_XREADY happens due to excessive transients in the circuit which I don't see anything to cause that So I only can think of three things:
1. The code is not properly written to write a register (I used the HAL library standard functions and I had to use the address 0x30 instead of 0x18 to connect to the chip, I attached the code too) here is what I do:
while(1)
{
RegisterAddress[0] = bq796x0_SYS_STAT;
recievedPack[0] = 0xDF; //Some random number in this format xx0x-xxxx
HAL_I2C_Master_Transmit(&hi2c2, bqI2CAddress, RegisterAddress, sizeof(RegisterAddress), MAX_I2C_TIME); //bqI2CAddress = 0x030 (="0x18")
HAL_I2C_Master_Receive(&hi2c2, bqI2CAddress, recievedPack, 1, MAX_I2C_TIME); //MAX_I2C_TIME = 10
HAL_UART_Transmit(&huart2, recievedPack, 1, 10); //Here I receive 0x20 when I boot the chip with the boot switch
if(recievedPack[0] & bq796x0_DEVICE_XREADY) //bq796x0_DEVICE_XREADY = 1 << 5
{
HAL_Delay(1000); //Wait for a sec then try to rewrite the SYS_STAT register
recievedPack[0] &= ~(bq796x0_DEVICE_XREADY); //Write 0 in the DEVICE_XREADY bit : xx0x-xxxx
HAL_I2C_Master_Transmit(&hi2c2, bqI2CAddress, RegisterAddress, 1, MAX_I2C_TIME);
HAL_I2C_Master_Transmit(&hi2c2, bqI2CAddress, recievedPack, 1, MAX_I2C_TIME);
//here I tried to use the "write without the repeated start" mode but I got nowhere
//recievedPack[1] |= bq796x0_DEVICE_XREADY;
// recievedPack[1] &= ~(bq796x0_DEVICE_XREADY);
// recievedPack[0] = bq796x0_SYS_STAT;
// HAL_I2C_Master_Transmit(&hi2c2, bqI2CAddress, recievedPack, sizeof(recievedPack), MAX_I2C_TIME);
}
HAL_Delay(200);
}
2. The resistors in series don't simulate the battery pack good enough.
3. The chip is damaged and I should change it with a new chip. (Actually, this might be possible since the LDO voltage is 3.8! Is there any way I can be sure of it?)
Any hint on what to do or how to find the source of the error is appreciated.
Thank you,
Best regards,
Arash.(Please visit the site to view this file)