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BQ25886: BQ25886 Battery UVLO threshold

balaji p1
Prodigy 110 points
Part Number: BQ25886
Other Parts Discussed in Thread: BQ25883

Hi,

with reference to BQ25886 datasheet page no 14:

8.3.1 Device Power-On-Reset

The internal bias circuits are powered from either VBAT or VBUS when it rises above VVBUS_UVLO_RISING or
VBAT_UVLO_RISING. When VBUS rises above VVBUS_UVLO_RISING or BAT rises above VBAT_UVLO_RISING, the BATFET
driver is active.

The Electrical parameter for "VBAT_UVLO_RISING" is provided as: 3.3V (Typical) and I couldn`t find value for "VBAT_UVLO_RISING"

VBAT_UVLO_RISING is actually the battery cutoff voltage where the BATFET driver is switched off when battery voltage falls below this value.

This protects the battery from deep discharge or battery depletion.

Whether i can consider VBAT_UVLO_RISING value also as same as VVBUS_UVLO_RISING.

kindly clarify about battery UVLO threshold.

regards

Balaji.P

  • 0
    TI__Genius 10385 points

    Balaji,

    VBAT_UVLO_RISING is the minimum voltage needed to bias the internal circuitry of the chip.

    I would not consider this a deep discharge protection scheme, but rather a physical requirement of the IC.

    BQ25886 does not have the integrated over-discharge of its sister parts (see BQ25883 section 8.3.13.2). I strongly recommend you implement an external over-discharge protection scheme as a 2S battery pack at 3.3V is significantly discharged.

    Thanks,

    Ricardo 

  • 0 in reply to Ricardo
    Prodigy 110 points

    Hai Mr. Ricardo,

    Thanks for your reply.

    I understand your point on VBAT_UVLO_RISING.

    Further in BQ25886  datasheet page:14

    8.3.2 Device Power Up from Battery without Input Source
    If only the battery is present and the voltage is above UVLO threshold (VBAT_UVLO_RISING), the BATFET turns on
    and connects battery to system.

     

    I will be happy if I know the threshold value i.e minimum battery voltge which may turn BATFET to ON state.

    I couldn`t find the actual electrical value for that parameter for "UVLO threshold (VBAT_UVLO_RISING"

     

    Kindly clarify.

    regards

    Balaji.P

  • 0 in reply to balaji p1
    TI__Genius 10385 points

    Balaji,

    We do not warranty a value for VBAT_UVLO_RISING for BQ25886, but in my personal observations it is about 4V.

    I hope this resolves your issue,

    Ricardo

  • 0 in reply to Ricardo
    Prodigy 110 points

    Hai Mr. Ricardo,

    Thanks for your reply.

    As we plan to implement this charger IC for portable electronic device which works under battery, we need to know at what voltage BATFET drive is cut off and that`s why i am particular about it.

    I will be happy to know If your observed value is repetitive  based on your test of operation.

    i pray that this value should be added in the device datasheet for developers.

    regards

    Balaji.P

  • 0 in reply to balaji p1
    TI__Genius 10385 points

    Balaji,

    I think this may be a non issue.

    Refer to the functional block diagram on page 13. Looking QBAT (Q4) you can see there is a body diode present in that MOSFET. That MOSFET is the BATFET.

    When VBAT is below VBAT_UVLO_RISING you will still be able to supplement your electronics on SYS. The catch however is that SYS voltage will not be regulated to VSYS_MIN as the internal circuitry of the chip is not active.

    The voltage seen on SYS when VBUS and BAT are below their respective UVLO thresholds will be VBAT minus a diode drop.

    I hope this resolves your issue,

    Ricardo

  • 0 in reply to Ricardo
    Prodigy 110 points

    Hai Mr. Ricardo,

    Thanks for your reply.

    Regards

    Balaji.P