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BQ25758: soft-start and OCP protect mode

Tommy Tzeng
Genius 5760 points
Part Number: BQ25758
Other Parts Discussed in Thread: BQ25756, BQ25792

Tool/software:

Hi Sir,

we have customer with inquire and we not sure can meet this specification, thanks for your support and learn from you.

1. need soft-start function is require, and can the BQ25758 stop output after the protection function is trigger?

2. when the current reaches OCP, the output will turn off, when the over current is to relieve, the output will resume power. will the soft-start operate again at this time? if the IC restart, will the soft-start operate again?

  • 0
    Prodigy 150 points

    Hi Sir,

    I would like to add some explanation why I need to ask about this.

           Our application is to use the output of the Buck-Boost IC as the UPS power supply for another device.

           We have a situation that the output has inrush current and the OCP will be triggered when the device is connected instantly after the output voltage is stable after the IC is started.

           Almost ICs in OCP is hiccup mode and the behavior is that OCP is triggered and the output is stopped. After short time, the IC is started again, triggering OCP again, and the cycle continues, which will cause the device to restart all the time.

           The IC we currently use will stop output when OCP is triggered. The CPU must reset the IC before it can output again, and the soft-start mechanism will also be restarted, so OCP will not occur again.

  • 0 in reply to Hung HanTse
    TI__Mastermind 30915 points

    Hello Tommy, Hung,

    Thanks for being patient with this. I'm out of office on July 4th and 5th. I'll get back to you next week.

    Best Regards,
    Ethan Galloway

  • +1 in reply to Ethan Galloway
    TI__Mastermind 30915 points

    Hello Tommy, Hung,

    1. Yes, the BQ25756 has a soft start function and the BQ25756 will stop the output when a protection is generated.

    2. Yes, the soft start will start again here. The soft start will also operate again when the IC restarts.

    Let me know if that will work for your application and let me know if you have any questions about this.

    Best Regards,
    Ethan Galloway

  • 0 in reply to Ethan Galloway
    Prodigy 150 points

    Hi Ethan,

    Thanks for your feedback. I have some questions as show following.

    Q1: The output voltage default is 5V, I want to setting let the output voltage would be 13V when IC turn on beginning. 

    I don't want the IC output to be 0V->5V->13V. Can it do that?

    Q2: Base on Q1, How can do that, I setting the register VOUT_REG[0x04] to 13V befort EN_CHG[REG0x17]=1?

    Q3:In spec, I don't see anything about stop output voltage when OCP happen. The register of status and flag are didn't see any about OCP interrupt. How can I know that when OCP happen?

  • 0 in reply to Ethan Galloway
    Genius 5760 points

    Hi Ethan,

    got it, thanks for your reply, and could help us reply some quesiton below? thanks.

    Q1: The output voltage default is 5V, I want to setting let the output voltage would be 13V when IC turn on beginning. 

    I don't want the IC output to be 0V->5V->13V. Can it do that?

    Q2: Base on Q1, How can do that, I setting the register VOUT_REG[0x04] to 13V befort EN_CHG[REG0x17]=1?

    Q3:In spec, I don't see anything about stop output voltage when OCP happen. The register of status and flag are didn't see any about OCP interrupt. How can I know that when OCP happen?

    in addition, can BQ25758 and BQ25756 design calculation tool be shared?

    BQ25756-DESIGN-CALC.zip

  • 0 in reply to Tommy Tzeng
    TI__Mastermind 30915 points

    Hello Tommy, Hung,

    Q1. Could you set VOUT_REG to 13V before setting EN_CHG=1? This will make the charger go from 0V->13V.

    Q2. See Q1.

    Q3. The IBAT_OCP_STAT is in REG0x24[5].

    Tommy Tzeng said:
    in addition, can BQ25758 and BQ25756 design calculation tool be shared?

    Yes, you use the calculation tool for both ICs.

    Let me know if that answers your questions.

    Best Regards,
    Ethan Galloway

  • 0 in reply to Ethan Galloway
    Prodigy 150 points

    Hi Ethan,

    Thanks for your reply.

    Base on question 1, I totally agree with your said, but the EN_CHG=1 is default setting which mean the output turn on at the same time when VAC has power. How can I make sure that I set VOUT_REG to 13V before setting EN_CHG=1, thanks!

  • 0 in reply to Hung HanTse
    TI__Mastermind 30915 points

    Hello Hung,

    There's a workaround for this. You can pull the CE pin HIGH to disable the converter. Once you are ready to enable the converter and have set VOUT_REG to 13V, you can pull the CE pin LOW to enable the converter or you set the registers DIS_CE_PIN=1 and EN_CHG=1.

    The charger turns-on the converter when both the CE pin is LOW and EN_CHG=1. Writing DIS_CE_PIN=1 prevents the charger from reading the CE pin.

    Best Regards,
    Ethan Galloway

  • 0 in reply to Ethan Galloway
    Prodigy 150 points

    Hi Ethan,

    Thanks for share your experiences, it's help for me. Currently I don't have any question.

  • 0 in reply to Hung HanTse
    TI__Mastermind 30915 points

    Hello Hung,

    Thanks for working with us. I'm going to mark this thread as resolved.

    If you have any more questions, let us know by starting a new E2E thread.

    Best Regards,
    Ethan Galloway

  • 0 in reply to Ethan Galloway
    Prodigy 150 points

    Hi Ethan,

    Our products will use the two ICs BQ25792 (Charge IC) and BQ25758(Buck-Boost IC) at same time, but the two addresses are the same(0x6b), Is there any way to solve it?

  • 0 in reply to Hung HanTse
    TI__Mastermind 30915 points

    Hello Hung,

    There's no way to adjust the I2C addresses. I recommend using an I2C mux to communicate with the different ICs.

    Best Regards,
    Ethan Galloway

  • 0 in reply to Ethan Galloway
    TI__Mastermind 30915 points

    Hello Hung,

    One more thing, we will be coming out with a lower voltage spin of the BQ25758 that should have a different I2C address. The new IC should be out by the end of October.

    Best Regards,
    Ethan Galloway