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OPT3004: Spike on I2C SDA line after ACK bit

Terry Hu
Expert 3610 points
Part Number: OPT3004

Hi Team,

My customer test OPT3004 I2C waveform and found a spike on I2C SDA line after ACK bit.

The supply voltage for I2C bus is 1.8V and pull up R is 1Kohm.

They have tried to change pull up R to 2.2K, 4.7K, 10K. 

4.7K or 10K can suppress the spike level but Tr will fail(up to >1us). 2.2K can not suppress the spike well.

I2C function seems no problem, but my customer hope to find out countermeasure that can solve this issue.

Any advice from you are appreciated. Thanks!

Terry

Attached waveform as below.

  • 0
    TI__Expert 6800 points

    Hi Terry,

    Is this happening during or after the ACK? Is it possible that this is because the master is releasing the line and the device is pulling the line low to ACK, and the small time in between is due to the pullup resistor?

    Thank you,

    Brent Elliott

  • 0 in reply to Brent Elliott
    TI__Expert 3610 points

    Hi Brent,

    Thanks for your reply.

    My customer send more details of the I2C waveform as below. 

    I agreed with your opinion: "because the master is releasing the line and the device is pulling the line low to ACK, and the small time in between is due to the pullup resistor"

    Any countermeasure for this? Thanks!

    Terry

  • +1 in reply to Terry Hu
    TI__Expert 6800 points

    Hi Terry,

    This small spike between the bus being freed and the device pulling the line low is not an issue as long as it happens on a negative clock edge, which is the case since it is the ACK bit causing this.

    Thank you,

    Brent Elliott