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tca9535: master sometimes misses the slave，signal is abnormal

Henry_Wu
Prodigy 160 points
Part Number: TCA9535

the normal sigal should be as follows.

while when i connect the slave tca9535, the abnormal signal like this.

this tca9535 and the master are on different pcb.

How to fix this problem?

  • 0
    TI__Guru 62920 points
    Hi Henry,

    Does the waveform always look like this, or is it normal sometimes? Is there anything else on the board oscillating at the same frequency that may be coupling onto these signals? Could you please share your schematic with us so that we can review it?

    Regards,
    Max
  • 0 in reply to Miguel Robertson
    Prodigy 160 points

    Hi Max,

    The schematic is as follows.

    The two parts are on the different pcbs which are connected by cables.And the pullup resistor which i tried 4.7k .

    There is no clock signal nearby.

    .

  • 0 in reply to Henry_Wu
    Prodigy 160 points

    I measured the frequency . it is just 99khz almost as same as iic speed.

    Maybe the sda is coupled by scl signal? The distance between the two signals is 28mils.

  • 0 in reply to Henry_Wu
    Prodigy 160 points
    Luckly, my problem is fixed by update another tca9535. Maybe the tca9535 is broken down somehow.
  • 0 in reply to Henry_Wu
    TI__Guru 62920 points
    Hi Henry,

    Thanks for the update - I'm glad to hear the issue has been resolved. I agree that the waveforms look very much like coupling of the SCL line onto the SDA line. You're right that the unit could have been damaged in some way. It also could have been a soldering issue. If you wanted to debug this further, you could place the original device on a new PCB and see if the issue appears again with the same unit.

    Please let us know if you encounter any other issues related to this device.

    Best regards,
    Max