• State Resolved
  • Locked Locked
  • Replies 6 replies
  • Answers 2 answers
  • Subscribers 63 subscribers
  • Views 233 views
  • Users 0 members are here
Support feedback
Options
Options
Similar topics

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

BQ34Z100-G1: PACK- connection to PCB Ground? Also, CE pin to control LEDs in larger system?

Matthew Wolde
Prodigy 10 points
Part Number: BQ34Z100-G1
Other Parts Discussed in Thread: BQ34Z100, SN74HC164

At a previous job, we used the BQ34Z100-G1 battery gas gauge as part of a larger system (audio system which can be powered by battery or DC power supply, in which the power supply can also charge the battery).  I am refreshing my memory on this ASIC, but am I correct in remembering that the PACK- net would be the same "Ground" as the rest of the PCB (and the BAT- would only go to the battery pack negative terminal, as well as the gas gauge's AGND and GND)?

Also, I remember that the gas gauge would show the LED's full-time when the audio system was on, but they would turn off when the system was turned off--although the battery could be charged if the system were plugged into the wall outlet.  In the datasheets, the CE (chip enable) pin was connected to the REGIN pin (and the REGIN would be jumpered to the LED's after I2C programming)... If I control the CE pin with the audio system's power (within the voltage rating of the CE pin), would that be the best way to "turn off" the gas gauge LED's when the audio system was turned off?  Is there a better way to turn off the LED's when the audio system is turned off?  (I cannot remember what we did at my previous job.)

  • 0
    TI__Genius 12215 points

        Either Pack- or BAT- can be connected to vss of the device based on the setting of bit [GNDSEL] in Pack Configuration Register, please refer to the detail in page 28 of sluubw5a.pdf.

        It is not recommended to control the CE for LED display, as CE pin does not only controls the LED, but controls the whole power supply of the internal IC, if bq34z100-G1 powers up when the cell voltage is not stable, the error could be high, because this is a pack side gauge, supposed to be connected to power supply since the battery is shipped from factory.

  • 0 in reply to Steven Yao
    Prodigy 10 points

    Thank you for the response.

    The description on Page 28 discusses an "ADC", but which bit setting should I use if I want the coulomb counter to work properly with regard to the rest of the PCB?  Say again that it's an audio board (with opamps, amplifiers, voltage regulators, external power supply connection, battery charging circuitry, etc.), I would expect that the PCB's "Ground" would be the same ground as "PACK-" such that the coulomb counter would measure the current flowing from the PCB into or out of the battery (across the current-sense resistor)... Yes?

    I understand what you're saying about the CE pin... I think a better choice (specifically regarding the LEDs) is to use something (other than the momentary switch SW1 in the reference schematics) to control the LEDs.

  • 0 in reply to Matthew Wolde
    TI__Genius 12215 points

        My understanding to your concern is regarding the wholeness of the current from the battery to other part of the board, actually, this can be always measured via measuring the voltage across the SRP and SRN no matter Vss of bq34z100 is connected to PACK- side or BAT- side.

       The concern for connecting the BAT- and VSS is the extreme high current could causes extra noise to I2C communication, otherwise, connect BAT- with VSS is salutary for voltage and current measuring from the perspective of suppressing common mode noise interference.

       For lightening the LED as the way you wish, I think you can use external LEDs mode with SN74HC164 to control the LEDs, the CLK and DATA signal can be designed to be connected to SN74HC164 inputs when the battery is connected to your system

  • 0 in reply to Steven Yao
    Prodigy 10 points

    I wasn't (originally) really asking about the VSS pin of bq34z100 until you brought it up regarding an ADC... I was more concerned about where to connect the ground of my full system's PCB (of which the bq34z100 will be a part) and my best guess is that it should be connected to PACK- (otherwise how will the bq34z100 see any current going to and from the battery).  For example, I believe that the ground for the opamps on my audio board should be connected to PACK- since if I were to connect the opamps' ground to BAT-, then no current would flow across the sense resistor and the voltage difference between SRP and SRN would always be zero.  Correct?

    You are confusing me now regarding the VSS pin of the bq34z100... The evaluation board's schematics show what the VSS pin is connected to "AGND", which is then connected to BAT-, but you are now saying that this would actually be a bad thing?

  • +1 in reply to Matthew Wolde
    TI__Genius 12215 points

    Matthew Wolde

        Sorry, I have misunderstood the PCB as the PCB with the bq34z100, for the PCB with audio system, the GND should always be connected to the PACK- of the PCBA with bq34z100 on it.

        For the VSS of bq34z100, it could be connected to BAT- or PACK- based on the setting of [GNDSEL] bit, please reference TRM(sluubw5a.pdf) for details.

  • 0 in reply to Steven Yao
    Prodigy 10 points

    Hi Steven,

    Got it now--thanks!