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BQ25758S: BQ25758S as Buck Boost only

Muhammad Awais
Intellectual 720 points
Part Number: BQ25758S
Other Parts Discussed in Thread: BQ25758, TPS25751, TPS25730

Tool/software:

Hi TI,

We are designing single cell battery chargers and there will be a total of 20 battery charging ICs in parallel with 0.5A output. We would like to use simple battery charging ICs with 5V input and without any programming involved. Pleas note that our input if coming from PD charger. We are thinking to just use a 5V, 10A Buck-Boost regulator with input coming from USB-C PD. I would like to know if can use BQ25758S only as a 5V, 10A output and if yes then please help me to understand this chip before going with it please help me to answer these questions so that we may proceed accordingly. If BQ25758S can't be used as a Buck-boost only then please suggest an alternative PD compatible regulator;

1. I can see this BQ25758S is a Buck-Boost converter with Charger features as well and this is confusing me to think if we can use it only as a 5V output and without using battery charging feature. Please confirm. 

2. I have a quick look on this BQ25758S datasheet stating that the default output is 5V. Can you please confirm that we can safely use it to generate a 5V, 10A output? As per the datasheet equation (4) is showing how to set the max current limit. I am assuming that if we will use the 5mOhm then we may set the max current output limit to 10A. Please confirm?

3. Any recommendation for the PD chip to use along with BQ25758S. As you know our application is USB PD sink only. 

4. BQ25758S is not where available. Can you please confirm on its availability and time. I can see BQ25758 that is in stock that has even wider input range and I believe both are pin compatible. 

Kind regards,

Muhammad Awais

  • 0
    TI__Mastermind 30755 points

    Hello Muhammad,

    1. Yes, the BQ25758S provides a 5V CV output by default.

    2. Yes, this should work. You'll need to set the IOUT resistor to limit the output current to 10A.

    3. I think the TPS25751 will work here. Can you ask the TPS25751 team about using this part? The only thing that will need to programmed on the BQ25758S is the input current limit. There's a few things I'm curious about for the application:

    • Will the BQ25758S be providing power to all 20 battery charger ICs?
    • How will the battery charger ICs split the power amongst themselves?

    4. The BQ25758S is in stock at the TI.com store. Can you get the ICs from there when you click Request Sample at the bottom of the page?

    Best Regards,
    Ethan Galloway

  • 0 in reply to Ethan Galloway
    Intellectual 720 points

    Hi Ethan,

    Thanks for your answers. Here is my reply to your question:

    • Will the BQ25758S be providing power to all 20 battery charger ICs? 

    Answer: Yes, so we can charge the max of 20 devices with each at 0.5A. There could be a single or max of 20 at same time. We will be using 20 of BQ25170DSGR as battery charger chips. 

    • How will the battery charger ICs split the power amongst themselves?

    Answer: As all of 20 chargers will need 5V with 0.5Amax (normally 0.3A) each so we will set the BQ25758S to provide 5V @ 10A so that if all of the 20 charging ICs will be charging at one time then we should have the required amount of power. Let me know if it make sense to you. 

    Kind regards,

    Muhammad Awais 

  • +1 in reply to Muhammad Awais
    TI__Mastermind 30755 points

    Hello Muhammad,

    That makes sense to me. Thanks for the new information. The BQ25758S will work for providing the 5V/10A to the battery charger ICs here.

    Best Regards,
    Ethan Galloway

  • +1 in reply to Ethan Galloway
    Intellectual 720 points

    Thanks Ethan for your confirmation. 

  • 0 in reply to Muhammad Awais
    Intellectual 720 points

    Hi Ethan,

    I have a question related to BQ25758S Mode configuration. As I told before that our input will be 5 to 20V vis USB-C PD and the output is 5V and output current can reach max up to 10A. As per this BQ25758S there is a physical MODE pin for configuring it by adding a pull-down resistor on MODE pin as shown below. Should I assume that we are going to use it in Buck-Only as our output will always be at 5V? If yes then what about the case when we only need like 0.5A and in this case our input from USB-C is only 5V so does this regulator works fine with 5V input and 5V output in buck only configuration?

    What is the difference between these buck modes? Any specific one we should be using? 

    We are adding TPS25730 for PD controller that has physical pins to set the Vin min and max along with current. Do you think it make sense to set it to Vin min of 9V and Vin max to 20V for PD input and then on BQ25758S we just use it as Buck only?

    Thanks and regards,

    Muhammad Awais

  • +1 in reply to Muhammad Awais
    TI__Mastermind 30755 points

    Hello Muhammad,

    Muhammad Awais said:
    Should I assume that we are going to use it in Buck-Only as our output will always be at 5V?

    Buck-only mode would make sense for your application.

    Muhammad Awais said:
    If yes then what about the case when we only need like 0.5A and in this case our input from USB-C is only 5V so does this regulator works fine with 5V input and 5V output in buck only configuration?

    You can use bypass mode here. Setting EN_BYPASS=1 will set the high side FET to always be ON. This will pass the VIN voltage directly to VOUT.

    Muhammad Awais said:
    What is the difference between these buck modes? Any specific one we should be using? 

    These modes are for the different inductor values. You'll need to use the mode that matches your inductor.

    Muhammad Awais said:
    Do you think it make sense to set it to Vin min of 9V and Vin max to 20V for PD input and then on BQ25758S we just use it as Buck only?

    This makes sense for the circuit. If you do this, you wouldn't need to worry about bypass mode.

    Let me know if you have any other questions.

    Best Regards,
    Ethan Galloway

  • 0 in reply to Ethan Galloway
    Intellectual 720 points

    Thanks Ethan for the reply and overall help. 

    Kind regards,

    Muhammad Awais

  • 0 in reply to Muhammad Awais
    TI__Mastermind 30755 points

    Hello Muhammad,

    Your welcome. I'm going to mark this thread as closed for now. Let us know if you have any more questions.

    Best Regards,
    Ethan Galloway