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TCA9555 SDA, SCL and INT pins

Richard Elmquist
Mastermind 45250 points
Other Parts Discussed in Thread: TCA9555

I have a customer that wants to use pull-up voltages above Vcc on the SDA, SCL and INT pins only. These pins are not really described in detail. I am assuming that these pins do not have pull-ups, but I am not 100% certain. Can you verify if using a pull-up voltage above Vcc (Vcc=2.5V; Vpullup=3.3V) on the SDA, SCL and INT will cause an issue? Can this damage the part in any way?

From what I have read in the forums it appears that the Icc of the TCA9555 might increase in this situation. Is this true? Can you verify the increase that they might see and why?

Can you send me a picture of these inputs showing the FETs etc.?

Thanks for your help with this!

Richard Elmquist

  • 0
    TI__Mastermind 45250 points

    Has anyone had a chance to look at the request above?

    Can you give a time frame as to when you might be able to provide the information?

    Thanks for your help with this!

    Richard Elmquist

  • 0 in reply to Richard Elmquist
    TI__Mastermind 23196 points

    Hello Richard,

    I can confirm that if you will not damage the parts when using pulls ups higher than Vcc as long as you don't exceed the max operating voltage of the TCA9555.  There is a leakage path and it will increase the Icc of the part as stated in the datasheet.

    I would like to know why the customer did not connect the Vcc to the same as the pull-up resistor voltage?  Is there any application reasons they did this for?  If there is a meaningful reason they do this it would be good for us to know. 

    -Francis Houde

  • 0 in reply to fhoude
    TI__Mastermind 45250 points

    Francis,

    The customer gave no reason for the variation in Vcc voltage above the Vcc used in the TCA9555.

    Can you explain why there is a leakage voltage? Is there a pull-up internal to the part? The customer would just like to understand why the leakage would increase in this situation.

    Thanks for your help with this!

    Richard Elmquist

  • 0 in reply to Richard Elmquist
    TI__Mastermind 45250 points

    Francis,

    Have you been able to verify why there is a leakage current if Vpullup is a higher voltage than Vcc?

    I would just like to be able to explain this.

    Thanks for your help with this!

    Richard Elmquist

  • 0 in reply to Richard Elmquist
    TI__Genius 16510 points
    Hello Richard,

    Francis is out of the office.

    To answer your question,

    The leakage path is not quite as simple as a diode or pull-up resistor.

    In short, what happens is when the voltage on the input of SDA/SCL goes above VCC, there is a 100k series resistor it will go through, and then it must go through one of the body diodes to rail. So the leakage can be roughly calculated by:

    Ileak = (Vi2cport - 0.7 - Vcc) / 100k ohm
  • 0 in reply to Jonathan Valdez
    TI__Mastermind 45250 points

    Jonathan,

    Thanks so much for your response!

    That should close this.

    Thanks again!

    Richard Elmquist