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TIDA-010247: PACK+ pin for charge voltage detection

Vladislav Mocluza
Prodigy 60 points
Part Number: TIDA-010247
Other Parts Discussed in Thread: BQ76972

Tool/software:

Hello TI team,

I am designing a stackable 18S BMS based on TIDA-010247 reference design.

I noticed that PACK pin is connected to the BAT_TOP, not to PACK+. 

1. Correctly I understand that in this case, TIDA-010247 does not support detection of attached charger? Because TOS Voltage and PACK+ pin's voltage are always the same.

2. If I need to connect PACK pin to PACK+ voltage, can I use the same approach as for LD pin in this reference design? 

As on the picture below, where I use VD3 and VD4 to protect pin from negative voltage.

Best regards,

Vladislav Mocluza

  • 0
    TI__Expert 3860 points

    Hi Vladislav,

    Actually, the PACK and LD pin are connected to BOT BQ76972 for wakeup. Because, you would expect the BOT AFE to power MCU. 

    Kian

  • 0 in reply to Kian Lin
    Prodigy 60 points

    Hello Kian,

    Thank you for the answer.

    But I still have some questions:

    1. Is it possible to connect LD and PACK pins of TOP AFE with a way as on the picture above?

    2. I believe you mean the following schematic. Correctly I understand that in this case TOS-PACK+ delta always will be negative? Because PACK+ = 18S voltage while TOS of BOT AFE = 9S voltage.

    3. It is not completely clear from the schematic how exactly BOT AFE do wake up of MCU. Could you clarify it a bit?

    Best regards,

    Vladislav

  • +1 in reply to Vladislav Mocluza
    TI__Expert 3860 points

    Hi Vladislav,

    Sorry for the late response. I was on timebank due to public holiday. 

    1. It looks okay yo connect as the picture you showed.
    2. What does the TOS-PACK+ delta mean? Why will it be negative?
    3. I mean the aim of wake-up event is to wake the whole system. So the ideal sequence is charger attached -> AFE wake -> AFE LDO power up -> LDO power MCU -> MCU wake -> MCU enable the DC/DC. The MCU is powered by BOT AFE so i expect the charger attach event to wake the BOT AFE

    Let me know if any questions

    BRs

    Kian

  • 0 in reply to Kian Lin
    Prodigy 60 points

    Hi Kian,

    Hope you had a good time.

    1. Thank you for confirmation!

    2. There is PACK-TOS Delta in Reference Manual which is responsible for some protections and wake up after charger is attached. 

    3. Got it. thanks/

    BR,

    Vladislav

  • +1 in reply to Vladislav Mocluza
    TI__Expert 3860 points

    Hi Vladislav,

    Thanks.

    PACK pin voltage can be sized by changing the serial resistance. The measurement on PACK pin is done by periodically connecting the internal pull-down resistor. The pull-down resistor is 600k so you can back-calculate the serial resistance to avoid get a negative  PACK-TOS Delta value.

    Kian