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PCA9306: PCA9306 Capacitive Load & Rpu design questions

user4979899
Expert 3080 points
Part Number: PCA9306
Other Parts Discussed in Thread: TXS0102

Hi Sir,

I have some PCA9306 vs TXS0102 design for I2C level shifter questions need to clarify with you,
Please help on below questions, thanks

- I2C I/O data rate will be 400KHz only but design mostly define max will not faster than 2MHz.
  And the I2C bus will have to support 14 devices and long traces with expected capacitive loads up to 200pF.
  Base on these requirements, PCA9306 is the more suitable solution than TXS0102, correct?

- If my customer will design with PCA9306, please help to clarify below questions.
   1.Output rise time is determine by pull up resistor, correct?
   2.Recommand External pull up resistor of 1.8V & 3.3V to allow the data rate as 400KHz with output capacitance up to 240pF,
     Is it suitable to use below resistor value?

     Pull up resistor of 1.8V = 2.7K ohm
     Pull up resistor of 3.3V = 1.5K ohm

  • 0
    TI__Guru 73271 points
    "I2C I/O data rate will be 400KHz only but design mostly define max will not faster than 2MHz.
    And the I2C bus will have to support 14 devices and long traces with expected capacitive loads up to 200pF.
    Base on these requirements, PCA9306 is the more suitable solution than TXS0102, correct?"

    If you are trying to support speeds higher than 400kHz choose TXS0102, if you are at 400kHz or less then choose PCA9306.

    "1.Output rise time is determine by pull up resistor, correct?"
    Correct.

    "2.Recommand External pull up resistor of 1.8V & 3.3V to allow the data rate as 400KHz with output capacitance up to 240pF,
    Is it suitable to use below resistor value?"
    Side 2 supports up to 240pF. Side 1 supports up to 132 pF.

    Thanks,
    -Bobby
  • 0 in reply to BOBBY
    TI__Expert 3080 points
    Hi Bobby,

    If there will be 14 devices and long traces, TXS0102 also can handle it?
    And we can found the bus capacitance limit is 400pF for PCA9306, how about the bus capacitance limit for TXS0102?
    Thanks
  • 0 in reply to user4979899
    TI__Guru 73271 points
    Hey Anne,

    The 400pF bus capacitance limit is NOT due to the device, it is due to I2C standard. TXS0102 has the same limit in terms of how it operates, above 400kHz I2C allows 550pF so that would be the new limit above 400kHz....

    Neither device buffers (redrives the signals), they both use a pass FET architecture which means side 1 and side 2 are not buffered.

    "If there will be 14 devices and long traces, TXS0102 also can handle it?"
    This shouldn't be a problem as long as the VoL of the slaves can support TXS0102 without ringing above 30%VccA.

    Thanks,
    -Bobby