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TCA9548A: Connect TCA9548A and MSP430 with I2C (400kHz)

Sh.Sasaki
Guru 13625 points
Part Number: TCA9548A


Hi,

My customer wants to connect TCA9548A and MSP430 with I2C (400kHz).

TCA9548A requires "I2C clock low time" to be more than 1.3usec.

The MSP430 has an I2C clock low time of 1.25usec when using I2C at 400kHz.
Therefore, communication cannot be performed as it is.

When I checked with E2E below, there was a comment that "TCA9548A may be rounded up to 1.3us."

https://e2e.ti.com/support/microcontrollers/msp-low-power-microcontrollers-group/msp430/f/msp-low-power-microcontroller-forum/1129668/msp430f5419a-how-to-connect-to-tca9548a-with-i2c-400khz/4190891#4190891

Is the TCA9548A "I2C clock low time" rounded up to 1.3us?
Can they use the TCA9548A "I2C clock low time" at 1.25us?

Best regards,
Sasaki

  • +1
    Guru 318760 points

    The 1.3 µs value was copied from the I²C specification.

    The TCA9548A has no internal clock; its state machine is driven entirely by SCL. The setup time of 100 ns and the clock high time of 600 ns show that a faster clock will be no problem. (But there are no guarantees beyond the datasheet specifications, and you are likely to have other I²C devices.)

  • +1 in reply to Clemens Ladisch
    TI__Guru* 77381 points

    Clemen's is correct. Our device doesn't have an internal oscillator and doesn't look directly at a period, it is a state machine driven device. In general, for our I2C devices, you can operate as slow as you'd like and communication should, going outside the max speed (faster) we spec may not work though. 

    -Bobby