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BQ24133 UVLO

user766432
Prodigy 10 points
Other Parts Discussed in Thread: BQ24133

Hello

I want to design a charger with the BQ24133.

First question :
How works the UVLO ?

If the battery voltage (3 cells) is in a low voltage state and without any external power supply, is the BQ24133 always drive the MOSFET to the load ?

I don't see in the datasheet any stop condition about that.
The only thing I see is the UVLO but it is 3.6V and the 3 cells low voltage is about 9V. 
The AVCC is directly connected to VBAT via a diode so impossible with 3 cells to reach the UVLO condition.
How to reach this condition.

Second question :

I want to use the BQ24133 to power supply the load (without any external power supply)
May I use a button to tie to ground or to the VBAT the AVCC pin ?

If AVCC is tied to ground (UVLO detect) => the power MOSFET of the Battery is not driven => no power supply to the load.

If AVCC is tied to VBAT and VBAT is not enough (see the precedent question) => the power MOSFET of the Battery is not driven => no power supply to the load

If AVCC is tied to VBAT and VBAT is enough (see the precedent question) => the power MOSFET of the Battery is driven => power supply to the load is ok

Really thanks for your quick help.
Best Regards

Jean-Marc

  • 0
    TI__Expert 3160 points

    Jean-Marc,

    The BQ24133 will automatically switch the battery to supply system power when the adapter is removed. 

    When there is no adapter, VBAT voltage supplies AVCC via diode and will not enter UVLO -- you are correct.  In this condition, the bq24133 enters sleep mode when VAVCC drops towards VSRN, and when VACN-SRN drops to <300mV the BATFET (Q3) is turned on to connect the battery to supply the system power. 

    When the bq24133 enter UVLO, all circuits on the IC are disabled and external FET control cannot occur.  

     

    Please let me know if this answers your questions, or if I can provide more information. 

     

    Best Regards,

    Rachel