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Original question:

BQ24780S: The 3.3V power supply for BQ24780S

BQ24780S: Question about BQ24780S when the battery pack does not have a BATPRES output pin

Lumina Gui
Expert 2975 points
Part Number: BQ24780S
Other Parts Discussed in Thread: TPS3898, BQ24780

Hi TI Teams,

We have some question about the application of BQ24780S when the battery pack does not have a  BATPRES output pin. We have found a post about battery packs without BATPRES output pins, but still have some question.The details are shown as below:

E2E link:

https://e2e.ti.com/support/power-management-group/power-management/f/power-management-forum/1019606/faq-how-should-the-batpres-pin-be-connected-on-the-following-chargers-bq24770-bq24773-bq24780s?tisearch=e2e-sitesearch&keymatch=BQ24780S%25252520BATPRES#

Questions:

1) Did pin13 and pin14 of the BQ24780 have internal comparators? From the BQ24780S EVM schematic, we can see that there is an external independent comparator TPS3898 designed. If there is an internal comparator integrated, does it need to select only one of this external and internal comparator?

2) If the CMPIN and CMPOUT pin is used for detecting battery status, what needs to be set for SMBUS and how do the other registers need to be setting?

3) Does the R37 resistance value to 200KΩ is OK (the existing smart battery body detection pin has a 10K pull-down resistor)? And how to choose the R45 resistance value?

4) Does it possible to reactivate the battery by applying the CMPIN/CMPOUT pin in the case of battery overdischarge protection (battery voltage is 0)?

5) If the battery status is detected by the battery voltage at point 1, then pin13 and14 don't need to be used, can we directly using the battery voltage plus one MOSFET reverse processing to pin 15 can also realize the same function?

Thanks,

Kind Regards

  • 0
    TI__Genius 16740 points

    Hello Lumina,

    Lumina Gui said:
    Did pin13 and pin14 of the BQ24780 have internal comparators? From the BQ24780S EVM schematic, we can see that there is an external independent comparator TPS3898 designed. If there is an internal comparator integrated, does it need to select only one of this external and i

    1).Yes, you can use either the TPS3898 or you can connect BAT to CMPIN pin through resistor divider (R35/R36) and Connect bq24780 CMPOUT to bq24780/BATPRES pin.

    Lumina Gui said:
     If the CMPIN and CMPOUT pin is used for detecting battery status, what needs to be set for SMBUS and how do the other registers need to be setting?

    2). REG0x12[51]=0, If you are using the internal comparator, your schematic design will be similar to the EVM, except JP4,JP3, and JP1 will be installed, and JP5 and JP2 will not be installed.

    Lumina Gui said:
    Does the R37 resistance value to 200KΩ is OK (the existing smart battery body detection pin has a 10K pull-down resistor)? And how to choose the R45 resistance value?

    3). I don't see any obvious issue with using 200kΩ. R45 is used to program hysteresis when the polarity is HIGH.

    Lumina Gui said:
    Does it possible to reactivate the battery by applying the CMPIN/CMPOUT pin in the case of battery overdischarge protection (battery voltage is 0)?

    4).This method has not been tested, so I can not provide information on if this will work or not.

    Lumina Gui said:
    If the battery status is detected by the battery voltage at point 1, then pin13 and14 don't need to be used, can we directly using the battery voltage plus one MOSFET reverse processing to pin 15 can also realize the same function?

    5).This method has not been tested, so I can not provide information on if this will work or not.

    Best Regards,

    Christian.

  • 0 in reply to Christian Moyer
    Expert 2975 points

    Hi Christian,

    We still have some question for your reply, the details are as below:

    Christian Moyer said:
    2). REG0x12[51]=0, If you are using the internal comparator, your schematic design will be similar to the EVM, except JP4,JP3, and JP1 will be installed, and JP5 and JP2 will not be installed.

    Q: Applying CMPIN and CMPOUT with or without a comparator only requires the charger to set REG0x12[51]=0?

    Is it the same software setup to use an external comparator(like TPS3898) versus an internal comparator (CMPIN and CMPOUT)?

    Is there an application difference between this CMPIN/CMPOUT inputs and outputs for 2/3 cell batteries?

    In addation, from the pin description, the application of external separate comparator still needs to be connected to pins 13 and14, so what is the advantage of this external comparator since the internal comparator can do this application?

    Christian Moyer said:
    3). I don't see any obvious issue with using 200kΩ. R45 is used to program hysteresis when the polarity is HIGH.

    Q: We are confused for the "program hysteresis when the polarity is HIGH", can you elaborate on that? Or is there a  available document with this description?

    Christian Moyer said:
    4).This method has not been tested, so I can not provide information on if this will work or not.

    Q: When the battery pack does not have a  BATPRES output pin, is there much of this usage of applying CMPIN and CMPOUT to BATPRES? Or is there any problem for this application?

    Thanks,

    Kind Regards

  • 0 in reply to Lumina Gui
    TI__Genius 16740 points

    Hello Lumina,

    Lumina Gui said:
    Q: Applying CMPIN and CMPOUT with or without a comparator only requires the charger to set REG0x12[51]=0?

     This is my mistake I meant to put: REG0x12[15]=0. You will also need to setup REG0x3B[3:7] to meet your requirements.

    Lumina Gui said:
    Is it the same software setup to use an external comparator(like TPS3898) versus an internal comparator (CMPIN and CMPOUT)?

    Yes.

    Lumina Gui said:
    In addation, from the pin description, the application of external separate comparator still needs to be connected to pins 13 and14, so what is the advantage of this external comparator since the internal comparator can do this application?

    The internal comparator can only detect if the battery voltage is above or below one voltage reference point. The external comparator is a window comparator that can detect if the battery above or below two voltage reference point.

    Lumina Gui said:
    Q: We are confused for the "program hysteresis when the polarity is HIGH", can you elaborate on that? Or is there a  available document with this description?

    Please refer to the pin function section of the datasheet:

    The output polarity and deglitch time is selectable by SMBus.A  resistor is placed between CMPIN and CMPOUT to program hysteresis when the polarity is HIGH. 

    Lumina Gui said:
    Q: When the battery pack does not have a  BATPRES output pin, is there much of this usage of applying CMPIN and CMPOUT to BATPRES? Or is there any problem for this application?

    I think I was confused on your previous question, You can still use the BATPRES pin even if the battery pack does not have BATPRES output pin 

    Best Regards,

    Christian.