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BQ76972: Termistors on TS2 pin

Vadim Lebedev
Prodigy 160 points
Part Number: BQ76972

Tool/software:

Hello, 
The TRM on Page 72 Says:


I'm not sure to understand this correctly.  Does it mean that there is no way to put the chip in SHUTDOWN mode?

I've stacked design, with 2 chips sitting on the same I2C bus. 
So on production line i intend to put on of the chip in SHUTDOWN mode using RST_SHUT pin, and reprogram its I2C address to 0x20.

Given the fact the i have termistors on TS2 pins It seems that the TR implies that this approach is unviable.

 Thanks

Vadim

  • 0
    TI__Genius 17755 points

    Hello Vadim,

    Vadim Lebedev said:
    Does it mean that there is no way to put the chip in SHUTDOWN mode?


    That note is referring to our ‘Soft Shutdown State’, which can be entered when the SHUTDOWN sequence is initiated and the TS2 pin remains LOW. More information on it can be found in this What is the Soft SHUTDOWN State FAQ. This SHUTDOWN mode FAQ also helps give more detail regarding SHUTDOWN mode.

    Best Regards,
    Alexis

  • 0 in reply to Alexis_H
    Prodigy 160 points

    Hi Alexis...
    Thanks for the pointers

    Afrer absorbing the info you've posted
    Here is the our schematic fragment



    And we have a thermistor on BOT_NTC2  net and a button on BOT_WAKE.

    It seems that we have a good chance to enter SOFT SHUTDOWN by accident:

    The most common reason for accidentally entering Soft SHUTDOWN mode is due 
to circuitry placed on the TS2 pin.  Placing a thermistor on the TS2 pin will directly 
pull the pin LOW, causing Soft SHUTDOWN, but even circuitry that does not pull TS2 directly
to GND can cause issues.  This is because the TS2 pin’s internal pull-up to 5V is 
very weak, so any small leakage paths in the circuitry attached to the TS2 pin can prevent 
SHUTDOWN by pulling the pin down.  
Even 1µA of leakage current can cause the device to become stuck in Soft SHUTDOWN.

    We do need to use SHUTDOWN mode for battery transport so we can't set SHUT_TS2 to 1  to avoid SHUTDOWN mode altogether.
    What would be your advice?    External pull up on TS2?

  • 0 in reply to Vadim Lebedev
    TI__Genius 17755 points

    Hello Vadim,

    If you want to use TS2 to enter SHUTDOWN mode, you can leave it floating or keep a switch/button for the Wake-up feature as shown in Figure 5-9. Schematic Diagram Monitor of the EVM User Guide. Other pins can also be configured as thermistor measurements as shown in Section 6.4 Multifunction Pin Controls of the technical reference manual.

    Best Regards,
    Alexis