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Original question:

TAS5766M: I2C interface

TCA9406: 5V I2C bus connection with 3.3V device (TAS5766M)

Akio Ito
Genius 3595 points
Part Number: TCA9406
Other Parts Discussed in Thread: TCA9517A, TAS5766M, , TCA9517, PCA9306

Hi,

I posted following question to audio amplifier forum.

A customer wants to connect TAS5766M with 5 volts I2C-bus he used to use. But TAS5766M is not able to connect with 5 volts I2C-bus directly, because SCL and SDA are not 5 volts tolerant terminals. Therefore he thought to put Level-Shifting I2C Bus Repeater such as TCA9517A between TAS5766M and 5 volts I2C bus. But VOL of TAS5766M does not satisfy VILC of TCA9517A. Is there any good solution?

The answer of audio amplifier forum was...
'We used the TCA9406 in one of our audio EVMs. You can take a look at this device.'

e2e.ti.com/.../2537413

The maximum VOL of 3.3 volts I2C slave device TAS5766M is 0.22 x VDD (= 0.762 V). Can we use TCA9406 in this case?


Best regards,

Akio Ito

  • 0
    TI__Guru 73331 points
    Hey Akio,

    TCA9517 is a buffer (it isolates capacitance on i2c lines) and typically buffers have static voltage offsets to tell which side is pulling low. This means our TCA9517 has an offset of about 500mV on B side when A side pulls low.

    TCA9406 is NOT a buffer but a voltage translator that supports 1MHz. This is important to know because it will basically pass what ever low from one side to the other side. If your TAS5766M pulls low down to 0.4V then both sides of TCA9406 will basically see that voltage.

    It sounds like TCA9406 or even PCA9306 will work as long as the 0.762V is okay for the receiving device.

    I will also state that just because the TAS5766M says the VoL is 0.22xVdd does not mean that it will reach this. The VoL is actually dependent on the pull up resistor. If you have a very small resistor (strong pull up) then you would see a large VoL like 762mV but if you use a large pull up resistor (weak pull up) then you will see a much lower VoL. So it could be possible the VoL of TAS5766M will be less than ViLc of TCA9517.


    Thanks,
    -Bobby
  • 0 in reply to BOBBY
    Genius 3595 points
    Bobby-san,

    Thank you for your answer. I also understand the actual VOL of TAS5766M depends on the value of pull-up resister.
    However, TI will not show the value of pull-up resister garanteed the VOL is less than 0.4 volts.
    I will recommend TCA9406 to our customer.

    Best regards,

    Akio Ito