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PCA9515A: I2C signals during unpowered state

Sreedev Krishnakumar
Prodigy 10 points
Part Number: PCA9515A
Other Parts Discussed in Thread: TCA9617B, TS5A23166

Tool/software:

Hi,

We are thinking of using PCA9515APWR in a design where we need to isolate I2C master and slave to prevent back powering issue. 

The design has limitations that the PCA can be powered only by slave VCC which is different from Master VCC. It is not possible to sequence Master and slave VCC.fp

Hence there is a good chance that SDA,SCL lines of the PCA on the master can be pulled up to master VCC before the PCA is powered on. 

Is it okay for the I2C lines to be powered up through pullups before PCA gets power?

Thanks.

  • +1
    TI__Mastermind 47668 points

    Hi Sreedev,

    This device does support powered-off high-impedance on the I2C pins, which would suggest that I2C SDA/SCL can be powered up before VCC. 

    I would recommend moving to the newer I2C buffer which is the TCA9617B. TCA9617B is the newest and improved cost structure for our I2C buffers. This buffer also supports powered-off high-impedance on the I2C pins,. level translation, and a smaller package type (8-pin VSSOP (DGK)). 

    Regards,

    Tyler

  • +1 in reply to Tyler Townsend
    Prodigy 10 points

    I see that the TCA devices have two power domains. VCCA and B. Is it okay to tie them together and use it for isolator application. Our system limitation means that I can connect only slave VCC to the isolator while the master has it's own separate VCC to which its I2C bus is pulled up.

  • 0 in reply to Sreedev Krishnakumar
    Guru 316860 points

    Using the same voltage for VCCA/B is allowed.

    If you just want to disconnect the slave bus when it has no power, you can use any switch with powered-off protection, e.g., TS5A23166.