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BQ76952: TI#BQ7695204 is abnormal at high temperatures

zehu chi
Intellectual 445 points
Part Number: BQ76952

Tool/software:

Hi TI engineer:

Regarding the TI#BQ7695204 IC: During the high-temperature static (no charging/discharging) storage test, we observed an abnormal phenomenon—when the ambient temperature gradually rises to 70°C ~ 75°C, the REG5.0V at Pin 34 of the TI#BQ7695204 IC suddenly powers down and then recovers abruptly. For detailed video footage of the REG5.0V fluctuation and some schematic diagrams, please refer to the attached. This phenomenon can be reproduced consistently on the same protection board.
Additionally, we have reproduced the exact same issue in multiple other projects that use the TI#BQ7695204 IC. This is not an isolated case but a widespread abnormality. We request that TI urgently confirm and investigate this issue, as it has affected our research and development progress
We eagerly look forward to your reply! Thank you!
  • 0
    TI__Prodigy 740 points

    Hi Zehu, 
    I replied to a similar thread with the same schematic, asking about the effects of no capacitor on REG2 output.
    What impact, if it is missing to place capacitor on regulator circuit REG2
    This could explain the issue you are seeing. 

    Without an output capacitor on the REG2 pin, you will likely see poor transient response and stability of the REG2 circuit, especially at higher temperatures.
    Additionally, 100 ohm series resistance of R1869 is not recommended unless you have some other system requirement for it.
    This may slightly degrade the line regulation and transient response of the REG2 circuit.

  • 0 in reply to Gavin Long
    Intellectual 445 points

    Hi Gavin

    We checked the datasheet and found there is a Shutdown Temperature register, whose default value is 85°C，when this temperature is reached, the Shutdown Temperature is triggered. We tried writing 0 to this Shutdown Temperature register, and afterward, no high-temperature power-off occurred even when the device was left idle at either 75°C or 85°C. Therefore, it seems that the previous high-temperature power-off issue at 75°C was caused by the activation of the Shutdown Temperature function. We have three questions:

    1. Does the Shutdown Temperature function appear to be enabled by default?
    2. The phenomenon occurred when the device was left idle at 75°C in a temperature chamber. Why is there such a large temperature error of 10°C?
    3. What is the NTC sampling accuracy of the BQ76952 IC for detecting the Shutdown Temperature?

    We eagerly look forward to your reply! Thank you!

  • 0 in reply to zehu chi
    TI__Prodigy 740 points

    1. Yes, the Shutdown Temperature function is enabled by default because the Power:Shutdown:Shutdown Temperature Register’s default is 85C.
    As you described earlier, if this register is set to 0 then the Shutdown based on measured internal temperature is disabled.

    2. Without calibration, other customers have seen a temperature error of 2-3C at room temp,  -5C error at ~50C, and -10C error at 67C. Without calibration, the gain error contributes much more to overall error at higher temperatures. This will depend on the Thermistor used, and the internal pullup resistance variation before calibration.

     BQ76952: Temperature measurement result is not accuracy when operating in high temperature 

    3. The datasheet (Section 12.2.3: Application Performance Plot) show a temperature error of up to ~3C with a specific Thermistor model.

    But some customers have seen Temperature of ~1C with correct calibration and calculated coefficients: https://e2e.ti.com/support/power-management-group/power-management/f/power-management-forum/998410/bq76952-temperature-accuracy-without-calibration

    For a detailed description of Calibration refer to Section 2.7 of the Calibration Guide and for Coefficient Calculation refer to the THERMISTOR-COEFF-CALCULATOR

    This post also walks through some Calibration troubleshooting: e2e.ti.com/.../bq76952-thermistor-value-shows-inaccurate-in-bq76952