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Original question:

BQ76952: PCB Design for SPI Communication

BQ76952: Problem with I2C Connection / REG1 0V

Alexis Kalk
Prodigy 40 points
Part Number: BQ76952
Other Parts Discussed in Thread: BQSTUDIO,

Hi,

i use  the BQ7695204 chip. The chip has SPI communication as default setup. I want to convert it to I2C-Communication.

I have updated my design with Matts comments and get my new PCB in the last days.

Unfortunately, i still measure 0V at Reg1 and at REGIN. I measure the power supply voltage (12V) before my transistor (2N 5551 Bipolartransistor).

In the last days, i made some experiments to concretise the problem.t

I used the microprocessor of the BQ76923EVM board to access to my "external" the bq chip. Its working if i supply the reg1 of the EVM-Board with 3.3V continously. BQ-Studio has detected my BQ76952 with SPI.

Then i changed the comm-protocol to I2C with OTP.

Now, the I2C dosnt work (i think beacause of the missing REG1 pull up) and i cant access to the bq-chip.

So you can find the schematic of the pcb (i have to made a small change in the implementation because i had only 1 diode at the moment.)

I will be grateful for any help.

Thanks

Alexis

BQ76952.pdf



  • 0
    TI__Guru 54715 points

    Hi Alexis,

    I don't see an issue with the board.  C6 is recommended to be 2.2uF, but that should not prevent talking to the part.    You have jumpers for the REG1 pull ups on the SDA & SCL.  If REG1 is off in the OTP you will need some pull up to talk to the part. Talking to the part may be a good step.

    Cycle power to the part after changing the interface and programming OTP.  Re-apply power and wake the part with S2.  Check that the REG18 has about 1.8V after wake.  

    On the EVM pull ups for I2C are provided by the 3.3V from the USB power.  If you remove the J3, J4 jumpers the load from REG1 should be disconnected and the EVM should be able to pull up the bus if you want to connect & talk from the EVM.  The EVM should allow you to enable the REG1 voltage and program OTP if  desired & allowed, remember there are limited writes.  If your MCU is powered by REG1 you would need it to come on when the BQ76952 wakes to power the MCU.  If the MCU has separate power that power should be able to provide the pull ups for I2C so that you can power the REG1 for other signaling.  

    If the EVM will not talk to the part with I2C you might check if it still talks on SPI.

  • 0 in reply to WM5295
    Prodigy 40 points

    Hi, thank you for your reply. Is the REG1 not enabled by default for BQ7695204PFBR?
    Unfortunately, SPI doesnt work anymore after OTP. I changed Commtype to "07" for I2C with OTP. May i change the IC?
    Thanks a lot 

  • +1 in reply to Alexis Kalk
    TI__Guru 54715 points

    Hi Alexis,

    Yes, BQ7695204 has the REG1 enabled, but once reprogrammed it will have the settings programmed.  I would expect if you changed only the interface that the regulator settings should have been the same and not changed in the OTP.  If they were cleared, when OTP was written the regulator was turned off.  OTP has limited writes, check to see if you can read the part with I2C with external pull up.  Check the regulator settings resulting from OTP, if cleared see if it will accept a reprogram.  If OTP can't be programmed to enable REG1 (and that is the setting you need) or if it won't talk anymore I think replacing the IC is the only option.

  • 0 in reply to WM5295
    Prodigy 40 points

    Hi again,

    i changed my chip with a BQ76952, which has I2C default. The REG12 are disabled by default.
    A question about OTP with BQ Studio, i can read on bq studio in the tab data memory. I unterstand, that it will change temporary if i "save" this changes with Write to Data Memory. For a permanent save, i need the OTP. I read in the documentation, that all the values are set up intialy to 0 in the OTP storage. First i make "read all" and "download" the factory settings in the BQ-Studio, than i make my changes on this configuration with "Write to data memory" and finally i say "Program OTP". In that moment, the data memry will be copied to the OTP memory. Is this procedure right?
    I want to enable the REG1 with 3.3V with OTP. I seen on bqstudio REG1 and REG2 settings are together in a byte registered. Bit0 is to disable or enable Reg1. But i didnt realy understand how to set up the voltage level with the rest 3 bits. I would like to set up it to 3.3V. Which will be the correct setup for this 3 bits. I think its 101 but im not sure. A confirmation will be great.


    Thanks

  • 0 in reply to Alexis Kalk
    TI__Guru 54715 points

    Hi Alexis,

    Yes, the OTP programming is basically as you describe.  Set the voltage as recommended.  See the BQ76952EVM user guide section 3.6.2 OTP Programming for a process with BQStudio, or see the application note https://www.ti.com/lit/pdf/sluaa32 

    For REG1 settings see the technical reference manual.  The REG0 needs to be enabled if using the external voltage dropping transistor for REGIN.  See REG0_EN in section 13.3.2.3 Settings:Configuration:REG0 Config 

    REG1 is selected in the bottom 4 bits of the configuration register, see section 13.3.2.3 Settings:Configuration:REG0 Config.  If using BQStudio you can hover over the bits in the data memory location to show the equivalent document.  

    3.3V would be "6" for the bit field or 110, with the enable this would be 1101, or 0xD.  Leaving REG2 off the register value would be 0x0D