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Question for BQ77PL900 47pin purpose

March Jasper
Expert 2340 points
Other Parts Discussed in Thread: BQ77PL900

Hi  All 

I have question for BQ77PL900   Pack (47pin) purpose.

Now we have some trouble about this Pack (47pin) status .

This Pack (47pin) will some time change to  "High " status and we have current leak with some time.

【Question】 

1)  Could you tell us about this Pack (47pin) function purpose? 

2)  We can try analysis this issues by self , but we need more information about this pin internal structure.

    Could you tell us about  this Pack (47pin)  internal Block ?  

   For instance  

      Internal Pull up  /  Pull Down  Resister value?? .  Open Drain ??  Output Resister ?? ........

We want to judgment about this phenomenon,    " Device Broken  "  or  "  Some other reason (Resister Setting...?) "

If  you have some idea bout this one , could you give me your advice? 

Thanks and Regard

March Jasper   (  Sugimoto /  Japan Disty ) 

 

  

  • 0
    TI__Guru 54715 points

    The bq77PL900 PACK pin has 3 purposes:

    1. Alternate power pin to the BAT pin
    2. Charge FET source voltage reference for the driver
    3. Input to wake the part from shutdown mode when the voltage is greater than VSTARTUP

    The attached diagram shows the first 2.  There is a high resistance to hold CHG near PACK to keep the FET off during shutdown, and a diode from CHG to PACK as a result of the circuit structure. There should be no pull up from the PMS pin which might be implied from the datasheet block diagram or from the startup function.  Note that the startup threshold in the datasheet indicates the minimum voltage that will start all parts, a part could start at a lower voltage.

    Inspect the system circit schematic considering the diagram below.  If the circuit looks much like the datasheet diagram, leakage across the discharge FET can raise the voltage on CHG and PACK slowly until the startup voltage is reached and the part will wake up in standalone mode with the FETs on.  This requires operating current for the part as well as providing power to the system load which can result in unexpected battery drain.  If the circuit uses special switching, consider the diode effect between CHG and PACK to see if there is an unexpected pull up.  If the effect is on only one or a few boards, look for contamination on the board, or leakage or damage on the discharge FET or in the bq77PL900.

    bq77PL900 PACK pullup path.pdf 

  • 0 in reply to WM5295
    Expert 2340 points
    Hi

    Thank you very much this detail explain.
    I will explain to customer about this one with pull up path.

    Thanks and Regard
    March ( Japan Disty / Sugimoto )