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Original question:

BQ25798: BQ25789 Schematic review

BQ25798: which supply is main supply for system load? pmid or sys (battery application)

Yash Dave
Prodigy 70 points
Part Number: BQ25798

Tool/software:

In the charger IC, with battery application, PMID and SYS are provided. Out of these,

1) which one should we consider as the main output? 

2) And if we want a 5V output, how can we set the voltage of main output?

3) Does it provide a default 5V output?

  • 0
    TI__Mastermind 32286 points

    Hello,

    We were out off office on Monday 1/20, response may be delayed. Thank you for your patience

    Best Regards,

    Christian.

  • 0 in reply to Christian Moyer
    TI__Mastermind 32286 points

    Hello Yash,

    I'm sorry for the delay we were out of office 1/20/24.

    Yash Dave said:
    1) which one should we consider as the main output? 

    SYS is the main output. If VBAT<VSYSMIN, VSYS=VSYSMIN. If VBAT>VSYSMIN, VSYS will be slightly higher than VBAT. If reliable input voltage is detected on VBUS, PMID=VBUS.

    Yash Dave said:
    2) And if we want a 5V output, how can we set the voltage of main output?

     VSYSMIN can be set in REG0x00. This is the minimum value of the VSYS. As the battery voltage increases, VSYS will rise to be slighty higher than battery voltage

    Yash Dave said:
    3) Does it provide a default 5V output?

    No, The default value is based on the resistance tied to PROG pin.

    Best Regards,

    Christian.

  • 0 in reply to Christian Moyer
    Prodigy 70 points

    Hello,

    I need some specs at my project:

     - 1S Li-ion battery =  3.7V

     - Vin = 5v

     - VSYS 5 V

    Can I use BQ25798 to generate VSYS = 5V ? Buck-Boost works to generate 5V with and without Vin?

  • 0 in reply to Yash Dave
    TI__Mastermind 32286 points

    Hello Yash,

    Please see my reponse from your previous thread:e2e.ti.com/.../bq25798-when-is-the-pmid-supply-used

    If you are using an Input voltage of 5V and a battery voltage of 3.7V, I would recommend using PMID as the system load. PMID will equal VBUS when in forward mode(5V). In reverse mode it will equal to the OTG voltage, This can be set to 5V in REG0x0B  

    In your case the reason why I would not recommend the SYS pin, is that VSYS_MIN should not be set greater than the max battery voltage. If you are using a battery voltage of 3.7V, VSYS should not equal 5V. 

    Best Regards,

    Christian.