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PCA9515A: about solution selection

Vera Mao
Expert 5065 points
Part Number: PCA9515A
Other Parts Discussed in Thread: PCA9515, TCA9517,

Hi  dear supporting team,

my customer has below application scenario, they need use FPGA GPIO port to drive a I2C bus, there are around 7 slave on the bus, highest rate is 400K, around 200pF cap on the load. but in FPGA side they can't add pull up resistor,  they want to use PCA9515 as a driver,  is it ok for this chip to operate in such scenario? tks a lot!

  • 0
    TI__Genius 17245 points

    Hello Vera,

    I want to make sure I understand your question.  Are you saying that the FPGA can't be configured as an open drain?  I2C is a bidirectional open drain architecture.  Can you explain why they can't have a pull up resistor?

    -Francis Houde

  • 0 in reply to fhoude
    TI__Expert 5065 points

    Hi Houde,

    thank you for reply!

    FPGA  GPIO port can have a pull up resistor, while it can not be configured as an OD port.  if so, what's the solution for such kind of application? tks!

  • 0 in reply to Vera Mao
    TI__Genius 17245 points
    Hello Vera,
    I haven't seen an FPGA that can't be configured to OD. Are you sure about this? Having a push pull will be ok on the SCL line assuming you don't have to support clock stretching but the SDA needs to be OD. How is the pin configured now? You must toggle from output to input correct?
    -Francis Houde
  • 0 in reply to fhoude
    TI__Expert 5065 points

    hi Houde,

    in the other way, if they could set it to OD, is PCA9515 suitable for such application? or other solution will be better?
    and if they could not set it to OD, is there no solution from us to enhance the drive ability? tks!
    customer is using MPSOC FPGA, there are two IOs , one is like normal FPGA, the other is like ARM IO, I2C is at ARM side, the original information they got from the vendor is that it could not be set to OD. from the FPGA reference design, they are using PCA9544,  if this one could be used, does it mean that it is actually be OD port?

     

  • 0 in reply to Vera Mao
    TI__Genius 17245 points
    Hello Vera,
    It must be OD. That is the only way that pin can be bidirectional and work with the PCA9544.
    -Francis Houde
  • 0 in reply to fhoude
    TI__Expert 5065 points

    Hi Fhoude,

    if so, which solution is most suitable for such application?  tks!

  • 0 in reply to Vera Mao
    TI__Genius 17245 points

    Hello Vera,

    I would look at the TCA9517 first.  It really depends on a variety of things.  Do you need translation/level shifting?  What is your Vcc for master and slaves?  Do you have size constraints?  VOL of both Master and Slave devices?  Generally speaking this part is a good fit.

    -Francis Houde

  • 0 in reply to fhoude
    TI__Expert 5065 points

    Hu Fhoude,

    thank you for the recommendation!

    for your questions:

     Do you need translation/level shifting?--- no

      What is your Vcc for master and slaves?---both are 3.3V

      Do you have size constraints? ----no

    VOL of both Master and Slave devices? ----both are around 0.4V

    and need drive 200pF cap load. 

    because they don't have AVL code of TCA9517 in their company, they can only make choice btw PCA9515 and PCA9548.  pls help confirm which one is better for such application, or TCA9517 is a must.  thanks a lot!

  • 0 in reply to Vera Mao
    TI__Genius 17245 points
    Hello Vera,
    I am assuming they don't want to qualify another part. The PCA9515A is the only option then, make sure that they are ok with VOL limits of the part. They need to check master and slave devices to make sure there aren't any VOL and VIL incompatibilities. The PCA9548 is a I2C MUX not a buffer.
    -Francis Houde