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TCA9800: I2C buffer integrated current source to VCC

Michiaki Tanii
Expert 4610 points
Part Number:

Hello team,

 

Could you please support the below inquiries from our customer ?

 

-        Where I2C buffer will be connect to is pulled down at 4.7k ohm for both SCL and SDA.
We have I2C buffer integrated current source pulled up to VCC such as TCA980x.
In case that where I2C buffer will be connect to is pulled down, could customer apply the I2C buffer integrated current source to their system ?
Or would be there possible to apply TCA9800 (0.54mA) to such above system ?
4.7k ohm * 0.54mA = 2.54V < Vcc = 3.3V                           would be OK ?
4.7k ohm * 1mA = 4.7V > VCc                              NG

 

-        In case that both master and slave is 3.3V and it has two slaves, the below connection is acceptable for our I2C buffer ?
And could you advise that it would be acceptable depend on integrated current source or not ?

 

-        Here is their requirements

  • 3.3V acceptable
  • More than 400kHz
  • Can interface with it pulled down resistor at 4.7k ohm.

 

If we have any recommendation devices, please give us your proposal.

 

Thank you and best regards,

Michiaki

  • 0
    TI__Guru 73271 points

    Michiaki Tanii said:

    Part Number: TCA9800

    Hello team,

     

    Could you please support the below inquiries from our customer ?

     

    -        Where I2C buffer will be connect to is pulled down at 4.7k ohm for both SCL and SDA.

    [Bobby] You mean on the left side? Technically both sides of the buffer will have an SDA/SCL line. I don't understand the 'pulled down' part of the statement. In I2C, SDA is always going to be pulled down from both directions since it is bidirectional. SCL would be the same as well though mostly it is unidirectional and would still be pulled down by the buffer.

    Are you saying pulled down as in the Vcc will not be present and force the I2C bus to GND?

    Or are you saying you plan to place a 4.7k resistor to GND? If so, why?


    We have I2C buffer integrated current source pulled up to VCC such as TCA980x.
    In case that where I2C buffer will be connect to is pulled down, could customer apply the I2C buffer integrated current source to their system ?
    Or would be there possible to apply TCA9800 (0.54mA) to such above system ?
    4.7k ohm * 0.54mA = 2.54V < Vcc = 3.3V                           would be OK ?
    4.7k ohm * 1mA = 4.7V > VCc                              NG

    [Bobby] If you used a 3.3V current source, the voltage would never go above 3.3V unless there was some kind of energy storage and a switching component involved. A 4.7k resistor to GND connected to a 1mA current source referenced to 3.3V would never go to 4.7V

     

    -        In case that both master and slave is 3.3V and it has two slaves, the below connection is acceptable for our I2C buffer ?
    And could you advise that it would be acceptable depend on integrated current source or not ?

     

    -        Here is their requirements

    • 3.3V acceptable
    • More than 400kHz
    • Can interface with it pulled down resistor at 4.7k ohm.

     

    If we have any recommendation devices, please give us your proposal.

     

    Thank you and best regards,

    Michiaki

    Please see my initial comments above, I think I am misunderstanding the request.

    -Bobby