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BQ76952EVM: IIC SCL is pulled low

Cherry Zhou
Mastermind 22235 points
Part Number: BQ76952EVM
Other Parts Discussed in Thread: BQ76952, EV2400, BQSTUDIO, BQ76940, BQ76930

Hi team,

Here's an issue from the customer may need your help:

The BQ76952 is controlled via IIC using the CH341 module. When using IIC, set the frequency 20K, BAT voltage 38V, and the logic analyzer grabs the IIC waveform as shown in the following figure, where SCL is pulled down for a period of time by randomly resulting in the signal cannot transmit properly. And the customer has modified to pull up resistor to connect an external 3.3V pullup supply. But the problem persists. 

When don't connect to AFE, the waveform is as follows:

Could you help check this case? Thanks.

Best Regards,

Cherry

  • 0
    TI__Genius 11315 points

    Hey Cherry,

    The BQ76952 will hold the SCL line low to slow down communications if it needs more time. This is called clock stretching. The master device has to be able to support this. Can you make sure that the CH341 module you are using supports clock stretching?

    Thanks,
    Caleb

  • 0 in reply to Caleb Perez
    TI__Mastermind 22235 points

    Hey Caleb,

    Thanks for your help.

    They are checking whether CH341 module support clock stretching. 

    Also, there is a bython library of bqcomm in the example code on TI's web, which should be based on the EV2400? Could you help provide it?

    Thanks and regards,

    Cherry

  • 0 in reply to Cherry Zhou
    TI__Genius 11315 points

    Hey Cherry, 

    I contacted the individual who would have information regarding the BQComm library. I should receive a response by Monday. 

    Thanks,
    Caleb

  • 0 in reply to Cherry Zhou
    TI__Guru* 78563 points

    Hi Cherry,

    I just wanted to point out that they can use BQStudio with the EV2400 to send commands - there is a Command Sequence window where they can send individual commands and create scripts. This is demonstrated in the BQ769x2 Software Development Guide. I am pretty sure we will not be able to share the bqcomm library since it is not public software.

    Best regards,

    Matt

  • 0 in reply to Matt Sunna
    TI__Mastermind 22235 points

    Hi Matt,

    Thanks and currently the customer is attempting to use SPI for more operation. 

    Also they have an additional question: Is the clock stretching of the BQ76940 IIC a proprietary feature of the internal IIC design? This feature cannot be turned off externally, correct?  and do other families like the BQ76930, BQ76940 also have IIC clock stretching?

    Thanks and regards,

    Cherry

  • 0 in reply to Cherry Zhou
    TI__Guru* 78563 points

    Hi Cherry,

    The clock stretching on the BQ76952 cannot be disabled. Clock stretching is used on many devices.

    The BQ76930, BQ76940 family does not use clock stretching. 

    The SPI is also an option for the BQ76952, although it is a little more complex. The BQ769x2 Code Examples have SPI examples and there is helpful information in the BQ769x2 Software Development Guide. 

    Best regards,

    Matt