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PCA9515B: Confirmation Request of Waveform

Shinichi Inoue
Guru 21626 points
Part Number: PCA9515B

Tool/software:

Dear Specialists,

My customer is encountering communication error.

Could you please confirm whether the waveform is OK or NG?

The falling edge of SDA (slave side) is delayed compared to a good product,and it does not go low when SCL (slave side) rises,resulting in a NACK.

After device replacement and OK board, the falling edge of SDA (slave side) is early, and it goes low when SCL (slave side) rises, resulting in an ACK.

For details, could you please see attached file?

Question about PCA9515 .xlsx

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I appreciate your great help in advance.

Best regards,

Shinichi

  • 0
    TI__Mastermind 47188 points

    Hi Shinichi,

    To summarize the case, PCA9515B is missing an ACK bit in the NG case. 

    What is the VOL on both sides of the buffer during the NACK (NG) case? 

    The VOL needs to be <= VILC = 400mV in order to pass a LOW through the buffer. If the VOL is too HIGH, a LOW bit could be missed. Adjust PU resistors to be weaker to lower the VOL - i.e. change 2.2k PU resistors --> 3k or 4.7k and re-test the NG unit. 

    Regards,

    Tyler