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Original question:

TCA9803: Which VCC side, side A or side B should be connected to I2C master device?

TCA9803: Is the internal constant current changed between regular acknowledge action and after 100us clock stretching action?

Kazuya Nakai59
Guru 22295 points

Part Number: TCA9803

 Hello guys,

 One of my customers is evaluating TCA9803 for their new products.

 In the evaluation, they connected the master device to side A of TCA9803 and a slave device to side B.

 Also VCCA and VCCB are 3.3V.

 Then they faced I2C communication error after about 100us clock stretching only.

 They found the cause. The cause was SDA_B voltage falling speed is slower than regular acknowleage action.

 The phenomenon is happened only after the clock stretching.

 I know TCA9803 has internal constant current circuit for side B pulling up.

 Is the internal constant current changed between regular acknowledge action and after 100us clock stretching action?

 Your reply would be much appreciated.

 Best regards,

 Kazuya.  

  • 0
    TI__Guru* 79331 points

    Hey Kazuya-san,

    Do you have a scopeshot of the issue occuring?

    "Is the internal constant current changed between regular acknowledge action and after 100us clock stretching action?"

    This shouldn't be the case, the current source is expected to remain constant through operation.

    Is it possible that there is a series resistor between the TCA980x and the slave on SCL?

    Thanks,

    -Bobby

  • 0 in reply to BOBBY
    Guru 22295 points

     Hello Bobby,

     Thank you very much for your reply.

     Yes, I have the wrong waveform they took but they don't want to disclose it on E2E.

     So could you please tell me your email address because I'd like to send the waveform to you directly?

     Thank you and best regards,

     Kazuya Nakai.

  • 0 in reply to Kazuya Nakai59
    TI__Guru* 79331 points

    Yes, you can email me at duynguyen@ti.com

    -Bobby