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TPS65721: can I use it to supply my circuit from the battery?

Amilcare Barca
Prodigy 80 points
Part Number: TPS65721
Other Parts Discussed in Thread: BQ24071, TPS65070, TPS65217

Hi,

my question is the title of this post.

TPS65721 can be used to charge the battery and as a voltage regulator (DCDC o LDO) and use those voltages for my circuit (when an AC input is connected).

But how can I use my battery to turn on the IC and get the same voltages? In other words, is it possible to power the system while independently charging the battery? Like BQ24071 does.

Thank you.

  • 0
    TI__Mastermind 30280 points

    Amilcare,

    Yes, any device that has "Dynamic Power Path Management" can supply power to the system (SYS) and charge the battery (BAT) from the main supply (AC) simultaneously.

    The TPS6572x devices have DPPM, as described on page 51 of the datasheet:

    "When the current needed for the load and for charging the battery exceeds the input current limit, the voltage at SYS will collapse. The DPPM loop will reduce the charge current, such that the total current for the load and the charge current equals the input current limit. This is done as soon as the voltage at SYS drops 100 mV below the target voltage."


    This feature is borrowed from BQ- devices and integrated into most PMICs that have a battery charger (for example: TPS6572x, TPS65070, TPS65217)

  • 0 in reply to Brian Berner
    Prodigy 80 points

    Hi Brian,

    thank you for your answer.

    In this way can I supply my circuit from the SYS pin? In other words, the SYS pin works as an output voltage... right?

    If I clearly understand I can power on all my circuit with the battery by pressing the push-putton. Then the SYS pin is supplied by the charge coming from the battery.

    Thanks,

    Amilcare

  • 0 in reply to Amilcare Barca
    TI__Mastermind 30280 points

    Amilcare,

    Yes, for the TPS65721 you can use SYS as a supply for the system. This is the only PMIC with power path management that regulates the SYS voltage with an LDO.

    For other PMICs with power path management, the supply is usually provided to SYS through a load switch so it is un-regulated and not particularly useful.

    Please ensure that the load you apply on the SYS will not cause your system to go above the IAC-MAX sepc of 450mA.

  • 0 in reply to Brian Berner
    Prodigy 80 points

    Thank you for your answer Brian, and sorry for my delay.

    This IC is quite tricky for me. I have understood that there are 3 output voltage pins: VSYS, VDCDC1 and VLDO1 and I can use the one I prefer.

    VDCDC1 and VLDO1 are costantly regulated, while VSYS depends on battery voltage.

    I need just 3.3V to supply my board from the battery after I press the push button. But what I am not understanding is which pin I should use to get 3.3V.

    I think VSYS is not a good idea because it depends on battery voltage..

    Thank you,

    Amilcare

  • 0 in reply to Amilcare Barca
    TI__Prodigy 370 points

    Hi Amilcare,

    Brian is currently out of office at the moment. He will be able to get back to you on this next week. 

    Thank you,

    Jadyn

  • 0 in reply to Amilcare Barca
    TI__Mastermind 30280 points

    Amilcare, 

    On the TPS65721, VSYS1..VSYS0 = 10b, meaning "10 = the output voltage of the power path at pin SYS is regulated to 5 V"

    VSYS cannot provide 3.3V, but it is regulated.

    As a result, DCDC1 is your best choice to generate 3.3V

    LDO1 would be better for generating 1.8V, which is typically used to power I/O and sensitive analog circuitry.