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BQ76952: SPI communication with STM32

Danilo A.
Mastermind 29870 points
Part Number: BQ76952


Hi Team,

Our customer is using BQ76952 together with STM32F103RBT6 but the MCU can't communicate with the battery monitor. Initially, he connected the REG1, REG2, BREG and REGIN to GND as shown in the schematic diagram below. He then revised the connections of these pins and use the sample code of SPI for STM32 from the product page of BQ76952. According to him, 

After studying the content of the forums and the experience of others, I realized that I should feed REG1 through REGIN. In this way, should feed REGIN about 4.2V until 3.3V appear on REG1 pin.
After floating REGIN and BREG from the ground, we receive noise. When BREG floats and REGIN fed 3.3V, I have the output, but the voltage of some cells is wrong (i think this error have been because of our code). When I connect REGIN to BREG, we have an output but more error and noise. We have 5.5 volts in all modes on BREG pin. I think it should be floating BREG and fed 4.2V to REGIN until the REG1 3.3V, but when REGIN cross from 3.3V, noise level go upper.

Please advise, BREG floats and feed on REGIN? (Should i use the transistor?) Is there a principled method?
Meanwhile, thanks for the code, my friend find error on your code and he sends it back after being fully resolved.

7206.BMS_Sch.pdf

Regards,

Danilo

  • 0
    TI__Guru* 81035 points

    Hi Danilo,

    What is their setting for the [REG0_EN] bit in the REG0 Config register? If they are using a BJT to supply REGIN from the stack voltage, this bit should be enabled. If they are supplying REGIN directly from a different source, this bit should be set to zero and the BREG pin should be tied to REGIN. 

    Please let me know more about the error in the example code once you have more information.

    Best regards,

    Matt

  • 0 in reply to Matt Sunna
    TI__Mastermind 29870 points

    Hi Matt,

    Thank you for your response. We have received this feedback from our customer.

    From the bq76952 datasheet 12.3.2 section (and number 4 from my try list), I think REG0 is enabled by default in the BQ7695204. it's right?
    if REG0 is enabled by default, we have to use bjt. can we disable this pin without OPT programming?
    I've tried:
    1- BERG and REGIN pins was tied to GND (We hadn't any communication and data)
    2- Both pins were left floated (We hadn't any communication and data)
    3- Both pins were tied together (We had communication and data, but data was not correct)
    4- I left BREG float and supply REGIN directly. BREG had 5.5V. if REGIN supplied almost from 1.8~3.3V we have SPI communication and data. if we go upper than 3.3V or lower than 1.8V, noise appear on data.
    5- Both pins were tied together and supplied from 0~5.5V. I was scared, When I opened a current limiter 300mA sink from power supply, when I opened more 700mA~1A was sank. stop the test!!

    Our customer will provide the details of the error in the example code early next week.

    Regards,

    Danilo

  • 0 in reply to Danilo A.
    TI__Guru* 81035 points

    Hi Danilo,

    REG0 is enabled by default on the BQ7695204, so they can either use a BJT or they can disable the REG0 from their MCU. I am not sure what is happening on #5 in their testing. It looks like they may have damaged the device.

    Matt