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PCA9515A: tie both PCA9515 SCL0/SDA0 together is fine?

user4979899
Expert 3080 points
Part Number: PCA9515A
Other Parts Discussed in Thread: PCA9515, TCA9517, , PCA9515B, TCA9509

Hi Sir,

Below is my customer's design topology and plan to tie both PCA9515 SCL0/SDA0 together.

Is it fine for their design? or we need to take care anything.

Please help to advice.

Thank you

  • 0
    TI__Guru* 77381 points

    Hey Anne,

    Is there a reason the customer is choosing to use the PCA9515 over the TCA9517? You could do something like this if you place A side of TCA9517 to the master.

    PCA9515A has an errata stating it does not support clock stretching and we suggest moving customers to TCA9517 or PCA9515B instead (TCA9517 preferred over the PCA9515 series).

    This current configuration you have could cause oscillations if the loading conditions are too different. Our datasheet 9515 should not be connected to each other and I would advise moving to the 9517 if possible.

    -Bobby

  • 0 in reply to BOBBY
    TI__Expert 3080 points

    Hi Bobby,

    Below is the original design from my customer that they used NXP PCA9508DP as below topology.

    And found the fail waveform as below to make the I2C can't work well.

    So they are looking if there is any instead part from us can helping on the design which they can't change any layout.

    Do you think TCA9517 is fine for the design?

     

    CH1: PCA9508_5 B SCH

    CH2: PCA9508_5 B SDA

    CH3: PCA9508_5 A SCH

    CH4: PCA9508_5 A SDA

    If we remove PCA9508_6, then the waveform looks good.

    CH1: PCA9508_5 B SCH

    CH2: PCA9508_5 B SDA

    CH3: PCA9508_5 A SCH

    CH4: PCA9508_5 A SDA

  • 0 in reply to user4979899
    TI__Expert 3080 points

    Hi Bobby,

    Could you please help on it?

    Thank you

  • 0 in reply to user4979899
    TI__Guru* 77381 points

    "So they are looking if there is any instead part from us can helping on the design which they can't change any layout.

    Do you think TCA9517 is fine for the design?"

    Our TCA9517 does not support B side to B side connection like you currently you have unless you disable one of the parallel B sides.

    It may be possible to resolve this by replacing of the PCA9508s with TCA9509 and TCA9517 but I need to know the voltages on A side and B side of PCA9508= 5, 7, 9, 11 to verify B side is larger than A side by atleast 1 V.

    -Bobby

  • 0 in reply to BOBBY
    Prodigy 10 points

    hi Bobby

    I am Quanta EE Bosun.

    currently our VCCA and VCCB are both 3.3V

    But found someone had ask the same question about TCA9509 with same voltage for VCCA and VCCB

    https://e2e.ti.com/support/interface/f/138/p/888559/3285707#3285707?jktype=e2e

    and the asnwer is positive.

     

    So i just want to double confirm that if we can replace PCA9508_5 to TCA9509 and the whole SMBUS can work functionally or not?

     

    Really appreciate for your help

     

     

  • 0 in reply to Bosun Wang
    TI__Guru* 77381 points

    Hey Bosun,

    I did send Annie a reply offline on the topic but just for online readers. The TCA9509 can operate at VccA=VccB however it is outside of the datasheet spec and we do not guarantee the electrical parameters can be met at that operating condition.  I suspect the set up could work but the ViLc on A side may shift. If the master/slave on the A side is strong enough to drive below the ViLc of 9509, then it should fix the issue. You would probably want to remove the pull up resistors on A side to help lower the VoL on A side.

    -Bobby