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BQ76952: The following description

Jianping Tian
Prodigy 161 points
Part Number: BQ76952


There have been multiple unresponsive issues during debugging 76952, and currently the problem cannot be found. Therefore, there are a few questions that need to be consulted:
Does 1 76952 require sequential startup or default startup when powered on, such as the need to pull down the wake signal
What is the state of REG1 before power on without configuration, whether it is suspended or has internal pull-down,
When the 76952 is not working, the clock signal of the ARM side SCL flips (position I2X1_SCL in the figure below), but the 76952 side SCL_ AFE is in a no signal situation, is there an internal pull-down on side 76952. What is the pull-down impedance?
When debugging BQ76952, we found that during high current (20A) charging, the voltage in the first section was about 200mV higher than the other sections, which has been verified as the cause of non battery imbalance.
We will use 76952 for 15 strings, with a short circuit in the next section. The balancing method is passive balancing of parity controlled by the host, with the cell being the real battery cell. The problem is when the cell_ When balancing is turned on at 15 (VC14-VC16), Cell_ The voltage of VC13-VC14 increases by about 20-40mV. 76952 Passive Equalization Timing Introduction: During voltage sampling, the equalization of active and adjacent nodes will be disabled. (VC14-VC16) and (VC13-VC14) are not adjacent nodes, so theoretically, VC13-VC14 can still be sampled normally when (VC14-VC16) is balanced. But in the scenario of 15 series usage, due to a short circuit in the secondary section, (VC14-VC16) and (VC13-VC14) became adjacent sections. At this time, normal sampling during equalization will lead to low section voltage and high section voltage. How to handle this situation?
1. As shown in the figure below, we will use 76952 as a 15 string, with a short circuit in the secondary section. The balancing method is passive balancing of parity controlled by the host, with the cell being the real battery cell. The problem is when the cell_ When balancing is turned on at 15 (VC14-VC16), Cell_ The voltage of VC13-VC14 increases by about 20-40mV. 76952 Passive Equalization Timing Introduction: During voltage sampling, the equalization of active and adjacent nodes will be disabled. (VC14-VC16) and (VC13-VC14) are not adjacent nodes, so theoretically, VC13-VC14 can still be sampled normally when (VC14-VC16) is balanced. But in the scenario of 15 series usage, due to a short circuit in the secondary section, (VC14-VC16) and (VC13-VC14) became adjacent sections. At this time, normal sampling during equalization will lead to low section voltage and high section voltage. How to handle this situation?
We found that 76952 exhibited intermittent IIC communication when tested for high temperatures in a constant temperature box at around 80 ° C. This phenomenon can also be replicated by blowing 76952 alone with a hot air gun at room temperature,
Preliminary software investigation revealed a communication fault while reading voltage. During the IIC read operation, the host timed out waiting for ACK after sending the slave address, reporting a communication failure. After detecting IIC communication failure

  • 0
    TI__Expert 8526 points

    Hi Jianping,

    In response to your questions:

    Jianping Tian said:
    Does 1 76952 require sequential startup or default startup when powered on, such as the need to pull down the wake signal

    Yes, the LD pin should be pulled HIGH or the TS2 pin should be pulled LOW.  Please see Section 13 in the BQ76952 datasheet for more information: BQ76952 3-Series to 16-Series High Accuracy Battery Monitor and Protector for Li-Ion, Li-Polymer, and LiFePO4 Battery Packs datasheet (Rev. B) (ti.com).

    Jianping Tian said:
    What is the state of REG1 before power on without configuration, whether it is suspended or has internal pull-down,

    REG1 is disabled without configuration.  Please see Figure 1-11 in the Pin Equivalent Diagram app note for more information: Pin Equivalent Diagrams for the BQ76952, BQ76942, and BQ769142 (ti.com).

    Jianping Tian said:
    When the 76952 is not working, the clock signal of the ARM side SCL flips (position I2X1_SCL in the figure below), but the 76952 side SCL_ AFE is in a no signal situation, is there an internal pull-down on side 76952. What is the pull-down impedance?

    See Figure 1-14 in the Pin Equivalent Diagram.  SCL and SDA should also be pulled up by an external 3.3V voltage source and 10kOhm pull-up resistors.

    Jianping Tian said:
    When debugging BQ76952, we found that during high current (20A) charging, the voltage in the first section was about 200mV higher than the other sections, which has been verified as the cause of non battery imbalance.

    If cell balancing is desired, the BQ76952 can perform manual or autonomous cell balancing.  See Section 15 in the Datasheet.

    Jianping Tian said:
    We will use 76952 for 15 strings, with a short circuit in the next section. The balancing method is passive balancing of parity controlled by the host, with the cell being the real battery cell. The problem is when the cell_ When balancing is turned on at 15 (VC14-VC16), Cell_ The voltage of VC13-VC14 increases by about 20-40mV. 76952 Passive Equalization Timing Introduction: During voltage sampling, the equalization of active and adjacent nodes will be disabled. (VC14-VC16) and (VC13-VC14) are not adjacent nodes, so theoretically, VC13-VC14 can still be sampled normally when (VC14-VC16) is balanced. But in the scenario of 15 series usage, due to a short circuit in the secondary section, (VC14-VC16) and (VC13-VC14) became adjacent sections. At this time, normal sampling during equalization will lead to low section voltage and high section voltage. How to handle this situation?

    If cells outside of the adjacent cell measurement rule will also be affected by cell balancing, then I recommend implementing a host algorithm to disregard the cells that will also be affected by the unique configuration.  Since it seems like cells 2 spots away from the cell being balanced will be affected by a known voltage amount, this should be a predictable and regular behavior.

    I also cannot view the figure.

    Jianping Tian said:
    We found that 76952 exhibited intermittent IIC communication when tested for high temperatures in a constant temperature box at around 80 ° C. This phenomenon can also be replicated by blowing 76952 alone with a hot air gun at room temperature,
    Preliminary software investigation revealed a communication fault while reading voltage. During the IIC read operation, the host timed out waiting for ACK after sending the slave address, reporting a communication failure. After detecting IIC communication failure

    Please ensure that the MCU used can support clock stretching.

    Best,

    Andria