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TCAN1146-Q1: SDI Issue

Muwei Zheng
Intellectual 1580 points
Part Number: TCAN1146-Q1

Hi team,

Our customer is evaluating TCAN1146-Q1 on their board and they found SDI pin keeps in Low(see "Abnormal Waveforms" below) in communication. The problem solved when they replaced the IC to a new one(see "Normal Waveforms"). 

What is the possible reason of this issue?

Thank you,

Muwei Zheng

  • 0
    TI__Guru 53555 points

    Hi Muwei,

    The SDI pin is an input to this device and should have minimal impact on the signal that is being driven by the SPI controller. The only reason why the transceiver itself would impact the state of this signal is if the SDI pin were damaged and presented an excessive current path to GND. This would only occur if the pin was exposed to significant electrical overstress beyond the datasheet specifications that damaged the pin. 

    Apart from the SDI signal, the device appears to be responding appropriately, as the SDO pin relays the device ID which is the appropriate response to a massage of all 0s. It would be unlikely that this behavior would be shown if the SDI pin was damaged in this way. 

    • On the abnormal device, is it possible to measure the leakage current into the SDI pin when Vio is applied to it? Because this pin has an internal pull-up to Vio, we expect this current to be minimal (a few uA). 
    • Does the abnormal device exhibit any higher than typical current draws on any supply pin? A damaged digital pin will likely cause some excess current draw from Vio that could be measurably different from an undamaged device. 
    • Has the abnormal device been A-B-A swapped to ensure that the device itself is the cause of the issue? If this has not been done, it's possible that the connection to the IC was causing an external short to GND. 
    • Has this behavior been overseved on any other units or boards? If so, what is the quantity of failure? If this is an isolated case, please confirm the issue with an A-B-A swap and current measurements. 

    Let me know if you have any other questions in the meantime. 

    Regards,
    Eric Schott