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BQ76942: About the IIC parameter problem of bq76942

JH Zhang
Prodigy 190 points
Part Number: BQ76942

Tool/software:

Hi TI experts,

I set the speed of IIC communication between bq76942 and MCU to 400K, but when I tested the IIC waveform, I found that the delay of tSU:STA and tSU:STO did not meet the minimum 600ns requirement of the specification, as shown in the attached waveform.
The MCU pin is configured as hardware IIC, so I want to know what these two parameters are related to? How can I improve the circuit or code to meet the requirements of the specification? Do you have better suggestions?
If I do not modify any parameters, tSU:STA and tSU:STO are less than 600ns delay, will this have any impact on IIC communication? For example, IIC communication fails? Please let me know.
Thank you.

  • 0
    TI__Expert 4245 points

    Hello JH,

    A smaller pullup resistor could assist you. Can you please share your schematic and/or code you used?

    Best Regards,
    Alexis

  • 0 in reply to Alexis_H
    Prodigy 190 points

    Hi Alexis,

    As shown in the attached schematic, I used a 2K pull-up resistor. I also tried changing it to a 1.5K pull-up resistor, but the waveform comparison did not show any improvement. The code is not available for the time being.

    If I do not modify any parameters, and the tSU:STA and tSU:STO delays are less than 600ns, will this have any effect on the IIC communication? For example, will it cause IIC communication failure? Please let me know, I need to clarify this.

    Thank you.

  • 0 in reply to JH Zhang
    TI__Expert 4245 points

    Hello JH,

    This sounds like it could be an issue with your MCU. Could you verify this with the MCU vendor you are using?

    I could also not see the schematic you shared. I only see the waveform and part of the datasheet you shared from earlier.

    There will be effects on the I2C communication if the delays are less than 600ns. The device could essentially fail to recognize the stop/start signals without the appropriate time given

    Best Regards,
    Alexis

  • 0 in reply to Alexis_H
    Prodigy 190 points

    Hi Alexis，

    Sorry, I forgot to attach the schematic, I will add it now. My schematic design is 2K pull-up.

  • 0 in reply to Alexis_H
    Prodigy 190 points

    Hi Alexis，

    The strange thing is that tHD:STA, tSU:STA, etc. all meet the requirements of the specification, but the delay of tSU:STO is between 400~600ns. I tried to change the pull-up resistor to 1.5K, or increase the speed of the MCU hardware IIC pin, but there was no obvious improvement. Do you have better suggestions? Or are there other factors that affect this delay? Or do you have relevant documents to send me for reference?
    Looking forward to your reply, thank you.

  • 0 in reply to JH Zhang
    TI__Expert 4245 points

    Hello JH,

    Thanks for sending the schematic image. 

    It still looks like it is an issue on the MCU side relaying things too quickly, in which case we cannot help, unfortunately.

    Best Regards,
    Alexis