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WEBENCH® Tools/BQ25895: bq25895 query

Siddhesh Peshkar
Prodigy 160 points
Part Number: BQ25895
Other Parts Discussed in Thread: BQ25898

Tool/software: WEBENCH® Design Tools

Hi,

I am working on a battery powered application and looking for a PMIC with charging current of around 2.5A and USB type C. 

Accordingly, the continuous current requirement is around 5A, and might occasionally scale the 7A mark, for a few milliseconds. I have come across bq25895. The specs mentioned in datasheet  are 6A continuous discharge ( and upto 1 Sec discharge pulse of 9 A ) and i think bq25895 can be useful. But i would love to know more about this, the max permissible frequency for occurrences of high discharges and its effects on the system ( particularly the IC ). I have tried the Webench designer tool and it permits the design with my requirements Iin=3A. 

One thing that i noticed is that in datasheet it was mentioned that the system voltage will be maintained at a minimum level of 3.5V, which i am unable to understand. According to the block diagram, while discharging, the discharge FET, Q4, is turned ON which connects the system to the battery. This implies whatever the battery voltage is available will be at system as well, as long as there is no inbuilt regulator, which i doubt ( or is it mentioned with no current being pumped into the system). Please correct me if this interpretation is wrong. The reason for being concerned is the use of high discharge li ion battery, which operates at a plateau of 3.4V while discharging and hence the system voltage query. 

Thanks.

  • 0
    TI__Guru 57481 points
    The minimum system voltage (REG03[3:1]) applies when a valid adaptor is connected to VBUS. It does not apply when only battery is connected. User may change the minimum system voltage between 3.0V-3.7V via I2C with the default setting of 3.5V. Thanks!
    Please click "This Resolved my issue" button if this post answer your question.
  • 0 in reply to Ning T
    Prodigy 160 points
    So, when the battery is plugged in the system, and it is used as the power source, the sys voltage will be (Vsys-(Isys*11mOhms)) ?
    And could you please throw some light on the below query?
    The continuous current requirement is around 5A, and might occasionally scale the 7A mark, for a few milliseconds. I have come across bq25895. The specs mentioned in datasheet are 6A continuous discharge ( and upto 1 Sec discharge pulse of 9 A ) and i think bq25895 can be useful. But i would love to know more about this, the max permissible frequency for occurrences of high discharges and its effects on the system ( particularly the IC ). I have tried the Webench designer tool and it permits the design with my requirements Iin=3A.

    One more charger that i came across while searching is BQ25898. It is having similar specs but i zeroed down to BQ25895 due to the higher recommended discharge current ratings. Could you please assert this ?
  • 0 in reply to Siddhesh Peshkar
    TI__Guru 57481 points
    When only battery is present, VSYS=VBAT-BATFET voltage drop.
    Referring to 8.2.15.3 on the d/s, when the system is significantly overloaded (IBAT>IBATFETOCP=minimum 9A), the device latches off BATFET. User has to reset the latch-off condition and turn of BATFET.
    BQ25898 is in smaller WCSP package than the bq25895 in QFN package, so the current rating is lower. Thanks!
    Please click "This Resolved my issue" button if this post answer your question.