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BQ25756E: Testing the BQ25756E chip, encountered some problems need to consult, the questions are as follows:

ken chen
Prodigy 190 points
Part Number: BQ25756E

Tool/software:

Hi TI Team,

At present, I am testing the chip BQ25756E, and I need to consult you for some problems, which are as follows:

1. After configuring the register, power it on and off again. Can the register value be saved?


2, TS pin, battery temperature measurement NTC B value know whether there are requirements (3435/3950);

3, the chip is powered on, do not configure the register, the default setting of the dead time is what;


4, 29.4V input, 2.5A current charging, switching frequency set 600KHz, MOS tube temperature 98℃, measured the step-down test tube, found that there is a phenomenon of simultaneous on-off, please tell me how to optimize;

5, 6 series batteries, after the voltage is charged to 25V, there will be a similar hiccup phenomenon, the SW switch waveform is fluctuating, and the output current will change greatly at this time (current fluctuation exceeds 0.5A), please tell me whether this phenomenon is normal, and if it is abnormal, how to optimize it;

6. When IIC communication is not used, the input undervoltage protection is set separately by hardware. There is a 2V deviation between the calculated undervoltage protection value and the measured value (RAC1=1000K, RAC2=6.2K, RAC3=38.3K, range 25.82-33.48V), and the protection is turned off when the measured value is below 28.3V; and

7, in the process of testing the charging curve, the constant voltage charging process, there will be a current rise process, the current curve is not smooth, what is the reason?

8、Test the charging current curve, found that the constant voltage phase charge to 0.18A directly ended the charge, this is normal?

  • 0
    TI__Mastermind 20065 points

    Hello Ken,

    Thanks for working with this.

    1. The BQ25756E will not remember the register settings.

    2. We recommend a 103AT-2 10-kΩ thermistor.

    3. The default dead time is 45ns. You can find this in section 8.5.40 of the datasheet.

    4. I think the turn-on and turn-off time of the FETs may be too slow. I think there's three different options here. You can change out the FETs to something similar to the AON6380. You could increase the gate drive voltage and this will increase the gate drive current. Or, you could also increase the dead time.

    5. This may be related to the issue in question 4. I think solving question 4 will remedy this issue.

    6. The IC might be in VINDPM here. I'd recommend setting the ACUV a bit lower to account for this. This FAQ may be able to help

    7. When your termination current is below 2A, we recommend setting EN_PFM=0. Try setting EN_PFM=0 and see if that makes a difference.

    8. What's your termination current set to here?

    Best Regards,
    Ethan Galloway

  • 0 in reply to Ethan Galloway
    Prodigy 190 points

    8.The test found that the termination current is 180mA, and what is the termination turn-off current of the chip?

  • 0 in reply to ken chen
    TI__Mastermind 20065 points

    Hello Ken,

    Thanks for the info.

    What was the termination current you set for the charger? Did you set the termination current with a register or with a resistor?

    Best Regards,
    Ethan Galloway