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PCA9548A: Inquire - PCA9548A_ time delay tolerance evaluation with MCU and sensors

Jax Lin
Prodigy 40 points
Part Number: PCA9548A
Other Parts Discussed in Thread: MSP-EXP430G2ET

Hi Sirs

With PCA9548A, MCU would like to control 4 sensors with same I2C ID.

=> How to evaluate the I2C time tolerance are enough?

PS. Attached are the MCU, Sensors time index.

Sincerely

Jax

  • 0
    Prodigy 40 points

    Condtion--------------------

    MCU(Update) => MSP-EXP430G2ET demo kit

    Sensor(Standard mode)

     => Data hold time_max = 3450ns

     => Data setup time_min = 250ns

     => trise_Max = 300ns

     => tfall_Max = 1000ns 

  • 0 in reply to Jax Lin
    Guru 259570 points

    The values of the MCU do not conform to the I²C specifications. Which MCU is this?

  • 0 in reply to Clemens Ladisch
    Prodigy 40 points

    We change MCU to MSP-EXP430G2ET demo kit

    Sensor(Standard mode)

     => Data hold time_max = 3450ns

     => Data setup time_min = 250ns

     => tfall_Max = 300ns

     => trise_Max = 1000ns 

  • 0 in reply to Jax Lin
    Guru 259570 points

    These values are compatible with the limits specified in the I²C specification (for standard mode, i.e., up to 100 kHz). So all I²C-compatible devices will work. The MSP430 is I²C compatible.

    The PCA9548A does not change the timing. (It slightly increases the bus capacitance, but this is just the same effect as slightly longer traces.)

  • 0 in reply to Jax Lin
    TI__Mastermind 27233 points

    Hi Jax, 

    I agree with Clemens on what he has responded thus far. 

    I have included the I2C specs from the standard. Please let me know if you have further questions. 

    Are your Trise/Tfall times flipped?

    Regards,

    Tyler

  • 0 in reply to Clemens Ladisch
    Prodigy 40 points

    Hi Clemens

    1. Goal: Check MCU, I2C switcher, Sensor could follow I2C SPEC(provided by Tyler)

    2. According to SPEC, 

    a. Where to describe MSP430G2x53 to follow I2C compatible?

       => I only could find the I2C time index in USCI (I2C Mode) (above figure 20).

    b. Where to describe PCA9548A does not change the timing?

       => I only could find the I2C time index like chp6.6

       => Does it have switch delay?

    c. Sensor trise & tfall is recheck to following index

        Sensor(Standard mode)

         => Data hold time_max = 3450ns

         => Data setup time_min = 250ns

         => trise_Max = 1000ns

         => tfall_Max = 300ns 

  • 0 in reply to Jax Lin
    TI__Mastermind 27233 points

    Hi Jax,

    Jax Lin said:

    a. Where to describe MSP430G2x53 to follow I2C compatible?

       => I only could find the I2C time index in USCI (I2C Mode) (above figure 20).

    These timing specs from the datasheet look to be I2C compatible up to 400kHz. This looks good to me. Rise time is determined by external pull-up resistance and the strength of the open drain driver. 

    Jax Lin said:

    b. Where to describe PCA9548A does not change the timing?

       => I only could find the I2C time index like chp6.6

       => Does it have switch delay?

    page 7 of the datasheet shows the I2C standards that this device abides by to be I2C compliant. 

    When you are talking about switch delay, are you talking about the time it takes after a successful ACK for the switches to change state? I don't believe we spec this in the datasheet. 

    If you are talking about prop delay from switch input to switch output, this is defined in the datasheet.

    Jax Lin said:

    c. Sensor trise & tfall is recheck to following index

        Sensor(Standard mode)

         => Data hold time_max = 3450ns

         => Data setup time_min = 250ns

         => trise_Max = 1000ns

         => tfall_Max = 300ns 

    The sensor looks to be I2C compliant with the timing specs provided here. I compared these values to the standard mode of I2C, and the max and min timings are within the spec. 

    Regards,

    Tyler