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TCA6416A: Input resistance

user5163865
Genius 4060 points
Part Number: TCA6416A


Tool/software:

Hi,

Question
Can TI provide a graph showing the variation in input resistance of I/O ports?

Background
Due to a design error by the customer, the input port was left open when the product was shipped.
Only ICs with a specific date code had an error during shipping inspection, and the standby current consumption was 200uA. Normal products are 1uA.
This problem was solved by adding a pull-up.

According to the data sheet, the input current is 1uA max, so I think the input resistance is 3300000Ω min.
If this resistance becomes large, it becomes more susceptible to noise, and I suspect that the Pch-Nch FET of the OPEN CMOS input is penetrated, increasing the current consumption.

Therefore, the customer would like to confirm whether there is really a variation in input resistance (current).

It may be very difficult, but please consider this as the IC is used in mass-produced products.

Best regards,
Hiroshi

  • 0
    Genius 4060 points

    Sorry,
    As an additional question, could you please show me a diagram of what the internal circuit of the input port looks like?

    Best regards,
    Hiroshi

  • 0
    Guru 319620 points

    The input resistance does not change. What you're seeing are shoot-through currents flowing from VCC to GND. See [FAQ] How does a slow or floating input affect a CMOS device?

  • 0
    TI__Guru 54558 points

    Hi Hiroshi,

    No change in input resistance. The spec of +/- 1uA you are referencing is the leakage of the input in/out of the device. It should be small, since the input is a high-impedance CMOS input. 

    Given high-z CMOS input, please look at Clemens' reply concerning floating inputs. That document should also describe the internal structure at a high level. 

    Regards,

    Tyler

  • 0 in reply to Tyler Townsend
    Genius 4060 points

    HI Tyler-san, Clemens-san,

    Thank you for your support.

    "No change in input resistance."
    Does this mean that the input resistance hardly changes over time?
    (No/little change over time is useful information for customers)

    The customer's question is whether there is any manufacturing variation in the input resistance depending on the "date code."
    (Because the customer's system only has problems with certain date codes)

    If you have any data (histograms) on the input resistance at the time of manufacture, please provide it.

    I apologize for repeating my question, but I would appreciate your help.

    Best regards,
    Hiroshi

  • 0 in reply to user5163865
    TI__Guru 54558 points

    Hi Hiroshi-san,

    There is some variation in input resistance as a given in the manufacturing process. The input resistance of a CMOS input however is very large (in the Mohm range). 

    According to the datasheet, the leakage of the input pin is within +/- 1 uA. This would not affect the VCC to GND path of the CMOS input which is the result of the shoot-through current that the customer is seeing. 

    If the customer has pictures of the top side marking of a good unit and "bad" unit, I can double check if there are any variations between the devices, or confirm if they are legitimate parts from TI. 

    Regards,

    Tyler