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Queries on I2C level translater (TCA9406)

Stephen Thomas
Intellectual 710 points
Other Parts Discussed in Thread: TCA9406, TXS0102

Hi,

As per datasheet of TCA9406, Vil specification is mentioned as below

Q1) Please help us in interpreting the VIL value mentioned in the datasheet, is it absolute value of 0.15V OR VCC X 0.15 V?

 

As per datasheet,  any input voltage on TCA greater than 0.15V for logic 0 may cause the TCA to interpret it incorrectly (logic ‘0’ might be considered as logic ‘1’ as the input voltage falls in undetermined state)

We feel that 0.15V for “ VIL max” is very less value as digital circuits are prone to have higher noise.

 

As per datasheet,TCA9406 is compatible to I2C & SMBus protocol. Below are the I2C & SMBus specifications for ViL as per Page 75 of SMBus Specification, Version 3.0

 

Kindly let us know the value of “Vil max” to be considered in our design.

 

Q2) “VIL Max” will be dependent on respective voltage rails or VIL value for both ports depend on VCCA ?

 

Q3) In our design we have connected VCCA to 3.3V rail & VCCB to 5V rail. In this case what will be the “Vil max” for port A ?

 

Q4) Which logic family does TCA series belong to ?

 

Regards

Stephen

  • 0
    TI__Expert 5140 points
    Hi Stephen,

    I'm looking into this and will get back to you soon.

    Thanks,
    Siby
  • 0 in reply to Siby James
    Intellectual 710 points

    Hi Siby,

    Any updates?

    Thanks

    Stephen.

  • 0
    TI__Expert 5140 points

    Hi Stephen,

    Here are the answers to your questions regarding TCA9406:

    Q1) Please help us in interpreting the VIL value mentioned in the datasheet, is it absolute value of 0.15V OR VCC X 0.15 V?

    A: For the TCA9406, you can think of this device as our level translating switch for I2C. With that being said, our VIL max spec listed in order to correspond to our VOL spec later in the datasheet. If you were to have a higher VIL, then you would have a different VOL altogether.

    The way to account for this change would be to follow this equation: VOL = VIL + Voffset.

    This will allow you to design around the digital circuits that have a higher voltage due to noise.

    Q2) “VIL Max” will be dependent on respective voltage rails or VIL value for both ports depend on VCCA ?

    A: For this device, this will not be the case. It will mainly be dependent on the VIL value that is sent through the level translating switch. However, do keep in mind for other devices in our I2C portfolio, that VCCA/VCCB will account for changes in VIL spec.

    Q3) In our design we have connected VCCA to 3.3V rail & VCCB to 5V rail. In this case what will be the “Vil max” for port A ?

    A: In this case, it will not be dependent on the rails.

    Q4) Which logic family does TCA series belong to ?

    A: The TCA9406 is the same as the TXS0102 device, but made specifically for voltage translation of I2C. There isn't a family that the TCA series belongs to, but they refer to I2C devices (Buffers, translators, switches, and I/O expanders).

    Thanks,

    Siby