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BQ76952: CHG FET High and IC not communicating with MCU

Miguel Pena
Prodigy 65 points
Part Number: BQ76952
Other Parts Discussed in Thread: MSP430FR2355

Tool/software:

Currently I have attempted to communicate with the IC using the MSP430FR2355 and the example code however it has not worked. I get stuck on "__bis_SR_register(LPM0_bits + GIE);" leading me to belive that the IC is not communicating with the MCU. 

Heres a list of what I have observed:

  • CP1 outputting ~22V
  • REG18 outputting 1.8V
  • TS2 floating or outputting 0V
  • V1-3 are showing (3.7, 7.4, and 11.1) using a resistor ladder for testing
  • V16 is 11.1V
  • DSG gate low
  • DSG drain ~10.8V
  • DSG Source ~11V
  • CHG gate ~11V
  • CHG source ~10.8V
  • CHG drain ~10.8V

I am not sure what else needs to be measured but when running with the ESP32 I was able to communicate with the I2C however becasue of clock stretching it was outputting values that did not make any sense. I am honestly not sure what else to do, I have tried to get out of soft shut down mode by tying RST pin high <1s and also >1s but it seems to go back to that state by keeping CHG high. Any recomendations? 

here is my schematic

below is my code that I  am using

/cfs-file/__key/communityserver-discussions-components-files/196/MSP430fr2355i2c.zip

  • 0
    Prodigy 65 points

    I have also noticed that when I take it out of shut down mode via pulling RST_SHUT high >1s, TS2 will show about 3.6V when being connected to a multimeter probe, when back to floating it goes back to 0v. when a thermistor is connected it hovers 98mV. 

  • 0 in reply to Miguel Pena
    Prodigy 65 points

    I’ve added TS2 to a capacitor tied to ground to keep it awake and not go back into soft shut down mode when I plug RST_SHUT high. I do have a couple of questions however

    • What is the voltage that comes out of the zener diode resistor parallel network that is tied to the gate? For my system it seems like the 11V stack voltage is being sent into the gate at the other end of the parallel network which is tied to the gate of the FET. 
    • How does the system detect when there is a load or charge on the system? When my system exited shutdown mode and the CHG FET pin went low, the CHG FET was still high because of the voltage coming out of the zener and resistor. However when I sent in a test 5V into my DSG FET gate it was able to pass current into my test load. So how does this work? Should it come on automatically when a load is present and if so what should I be seeing at my LD and PACK pins? 

    I appreciate yalls help as this has been a struggling IC for a college student with not a lot of experience. I apologize for the constant simple questions and hope that you can keep helping me! Thanks!!

  • 0 in reply to Miguel Pena
    TI__Genius 17795 points

    Hello Miguel,

    Miguel Pena said:
    leading me to belive that the IC is not communicating with the MCU

    Do you have any logic analyzer files of the SCL/SDA lines? We also have a Software Development Guide and Sample Code here that can be referred too. Is that what you’re using?

    Are SCL/SDA lines measuring ~3.3V for both?

    Miguel Pena said:
    I have tried to get out of soft shut down mode by tying RST pin high <1s and also >1s but it seems to go back to that state by keeping CHG high. Any recomendations? 

    When you pull RST_SHUT high for > 1s, you are initiating the SHUTDOWN sequence (Shutdown Mode FAQ). This will unfortunately not help you exit Soft Shutdown Mode. Please refer to the Soft Shutdown FAQ for reference on how to leave it.

    Miguel Pena said:
    I have also noticed that when I take it out of shut down mode via pulling RST_SHUT high >1s, TS2 will show about 3.6V when being connected to a multimeter probe, when back to floating it goes back to 0v

    That is the correct voltage to expect around TS2 if there is still a power source connected to the BAT pin and the part enters SHUTDOWN. This is further discussed in Section 7.5 SHUTDOWN Mode of the technical reference manual (TRM). ~3.6V is what is expected at the pin with the voltage drop. 

    Miguel Pena said:
    How does the system detect when there is a load or charge on the system?

    Load is detected through the LD pin, whereas the charger is detected through the PACK pin. Please refer to the TRM for further information on it. This General FAQ may also be useful to refer too.


    I will need some time to review your schematic, however, please refer to Connecting battery cells to BQ769x2 family of monitors FAQ for cell connections and shorting cells. 


    Best Regards,
    Alexis

  • 0 in reply to Alexis_H
    Prodigy 65 points

    I do not at the moment however yes I have them connected to a 3.3v pull up resistor. I and still confused as to what should be coming out of CHG pin. At the moment I see 11V outputting and DSG is low. Maybe this is normal? I am not sure. I will try to get some readings soon!