The TI E2E™ design support forums will undergo maintenance from Sept. 28 to Oct. 2. If you need design support during this time, contact your TI representative or open a new support request with our customer support center.

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

BQ25792: About operation when the battery is removed during charging

Part Number: BQ25792
Other Parts Discussed in Thread: BQ25798

Hi,

We are doing various operation tests using BQ25972EVM.

Customer tested removing the battery during the charging operation.
As a result, BQ25792 acted as a momentary power failure of VSYS voltage.
VSYS stabilizes when CE is disabled or a battery is connected.
Could you tell me why the system voltage drops regularly if you remove the battery while charging?

Test condition is ;
・VBAT:4cell Ni-MH
・VBUS:5V/3A sauce
・VSYS load:30mA
・Vsys min = 5000mV
Charge Voltage = 6600mV
Charge Current = 1000mA
・IINDPM = 3000mA
VBAT=LOWV = 15%*VBATERG
・CE pin:enable
・WD:disable

We assumed that VSYS would be maintained if the battery was removed while the VBUS was connected and charging.
Customer want to provide a stable VSYS even when the battery is removed.



Regards,
Yusuke

  • Hi Yusuke-san,

    The 792 has fast charge startup that causes the small BAT capacitors to overcharge.  This results in BATOVP and then SYSOVP.  The OVP events cause the charger to disable the converter temporarily until the OVP event disappears.  If a battery (or large capacitor>470uF) is attached at BAT, this will not happen.  Also, if charge is disabled (for example when a battery with thermistor attached at TS or with CE bit or pin) , this will not happen.

    The BQ25798 does not disable the converter when SYSOVP immediately follows BATOVP.  I recommend moving to BQ25798.

    Regards,

    Jeff

  • Hi Jeff-san,

    Thank you for your support.
    I would like to consider introducing BQ25798.

    >The BQ25798 does not disable the converter when SYSOVP immediately follows BATOVP. 
    Is there an explanation in the datasheet for the above functions?
    I want to prove that the BQ25798 does not turn off the converter immediately after OVP.

    Regards,
    Yusuke

  • Hi Yusuke-san,

    There is no explanation in the datasheet about his feature improvement in the 798 vs the 792.  

    Regards,
    Jeff