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TCA9546A: SDA signal is permanently LOW at Power ON Condition

Rajat Singh
Intellectual 350 points
Part Number: TCA9546A

Hi Team,

We are using TCA9564 in one of our design as 2 channel configuration.

TCA9546 is working on VCC =3.3V level

Master SCL SFDA is at 3.3V and slaves side also working on 3.3V. so in this condition VPASS will be 3.3V

When I  probed on master side SCL, SDA then it seems like Signals(SCL,SDA) are at 3V so my queary is how this master side 3V level will impact slave side channel A and B?

If master side SCL SDA are 3V then what will be the VPASS voltage?

What can be the cause of SDA Low in starting condition?

Regards

-RS

  • 0
    TI__Mastermind 48988 points

    RS,

    Vpass is defined as the lowest pull-up voltage including the master side pull-up voltage. If the lowest pull-up voltage is 3.0V on the master side, the Vpass = 3.0V.

    This will help set the VCC of the TCA9564. 

    I roughly drew is out on the graph, but here is what I came up with.

    At Vpass = 3.0V, VCC is roughly ~4.4V. It is recommended that you set VCC = <4.4V in order for proper separation of the two sides during the idle phase of I2C. In your schematic, VCC = 3.3V (or 3.0V) so this should be ok. 

    Regards,

    Tyler