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BQ24133 - AVCC pin

Dice-K
Mastermind 6927 points
Other Parts Discussed in Thread: BQ24133, TPS61165

Hello,

I have questions about BQ24133.
When PVCC and AVCC are power-off, AVCC outputs the battery voltage.
Is this function correct?

If same behaviour terminals exist, please teach me the terminal names.

Regards,
Daisuke

  • 0
    Mastermind 6927 points

    Hello, everyone.
    Could you please answer this question?

    Regards,
    Daisuke

  • 0 in reply to Dice-K
    TI__Genius 13700 points

    Hello Daisuke,

    The voltage on AVCC is discussed in the Power Up section of the datasheet on Pg. 18 which stats that the battery voltage will be present on AVCC and only when there is a voltage present on AVCC that is greater than the battery voltage will the device exit sleep mode.

    I am not sure what you are asking in your second question could you please clarify?

  • 0 in reply to Ryan May
    TI__Expert 3160 points

    Daisuke,

    AVCC is an power input pin only.  If you are using the 133 EVM, you will be able to measure VBAT voltage on the AVCC pin due to the diode 'or' function.

    This ensure that the IC remains powered and in a known state even when the input adapter is removed. 

    In the typical application there is no true battery output pin.  The battery (VBAT) and system should be connected as below in the typical application diagram from the bq24133 datasheet (page 4): 

    If this still doesn't clarify your question, please give us some more details and Ryan or I will be happy to help. 

    Thanks!

    Rachel

  • 0 in reply to Rachel Moore
    Prodigy 185 points
    Hi,

    I have a questions regarding this AVCC pin as well. If I do not connect the Vbat to the AVCC pin but put a pull down resistor at the /BATDRV pin, can this still work? When there is no adapter plug in, the TPS61165 is in off state and and pull down resistor will turn on the Q3 MOSFET to connect the battery to the system. And when the adapter is plugged in, the TPS61165 will turn on and drive the /BATDRV high to turn off the Q3 MOSFET and connect the adapter to the system.

    Is my interpretation above correct? Is there any concern if I do it that way? Thanks.

    Regards,
    Lennon.
  • 0 in reply to Lennon Low
    TI__Expert 3160 points

    Lennon,

    It's not impossible to implement what you're describing, but it's not recommended. By connected VBAT to AVCC the bq24133 stays powered and can properly control the timing between on/off of Q1&2 and Q3. 

    By doing what you describe, the first concern that comes to mind is that the time between adapter remove and Q3 turn on could be longer in which case, all the system load is being drawn through the Q3 body diode which can cause excessive heating and damage Q3. 

    Is there a particular system requirement that you're trying to meet by making this change? 

     

    Thanks!

    Rachel

  • 0 in reply to Rachel Moore
    Prodigy 185 points

    Hi Rachel,

    Thanks for your reply. Sorry my previous question has typo on the MPN. It should be BQ24133 and lucky you understood what I meant.

    The reason of making this change is because we are trying to implement the application circuit on a 9V input to charge a 2-cell battery.

    At 9V, charging a dummy battery (power supply and a load), nominal fast charge current was set at 476mA. When the battery voltage charged higher than 7.8V, fast charge current dropped to below 50mA.

    To resolve the above issue, one way was to short out D1 to reduce the voltage from adaptor to AVCC. With this change, at 9V input, the charger behaved as expected, fast charge current was able to maintain at 476mA and started to drop when VBAT above 8.1V.

    However with this implementation, we are worried what would be the consequences of by not connection the VBAT to AVCC.

    With your explanation, it seems it is still recommended to connect the VBAT to AVCC. Should you have any other way to implement a 9V input charging circuit with this BQ24133 that can fast charge up until 8.1V before dropping, do recommend to me. Thanks.

  • 0 in reply to Lennon Low
    TI__Expert 3160 points

    Lennon,

      

    Is this a pure battery charger or charger + system?

     

    Thanks,

    Rachel 

  • 0 in reply to Rachel Moore
    Prodigy 185 points

    Hi Rachel,

    It is a charger + system. The end application is a handheld lighting tools (for automotive inspection or other lighting illumination purposes - something like a torchlight but with a string of high brightness LED).

    It runs on a 2-cell Li-Ion battery. BQ24133 is used to charge the battery in the system.

  • 0 in reply to Lennon Low
    TI__Expert 3160 points

    Lennon, 

     

    One potential option would be to eliminate the power path and connect the system to the battery node. Then you could leave out Q3 and not have to power AVCC from the battery.  You can see as example in Fig2 of the bq24133 datasheet:

    There are some limitations to this configuration; primarily you loose the DPM feature, and your system will not be able to turn if your battery is deeply depleted until it's charged up sufficiently (no instant on). 

    Thanks!

    Rachel 

  • 0 in reply to Rachel Moore
    Prodigy 185 points

    Hi Rachel,

    Thanks for your feedback. We will look into that possibility. Appreciate your help.

    Thanks again.