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TCA9517A: About VCCA> VCCB

Part Number: TCA9517A
Other Parts Discussed in Thread: TCA9517

Hi-Team

I have a question with TCA9517A.

From the contents below
"Deleted VCCA <VCCB from the Design Requirements list."
Is the following configuration possible?


I confirmed the contents of past E2E.
Under the condition that VCCA> VCCB difference is large,
I understood that it does not operate properly, but is it correct?

Best Regards,
Ishiwata

  • Hey Ishiwata-san,

    The configuration you've chosen will work. VccA only generates a reference voltage for the device, while VccB generates the reference voltage and drives the NFETs on SDA/SCL of both sides.

    Thanks,
    -Bobby
  • Hi Bobby

    Thank you your responce.

    I understand that your answer normal operation in the configuration I asked. Is that understanding correct?

     3.3V           5.5V              3.3V
     Master―――― A-side TCA9517A B-side ―――― A-side TCA9517A B-side ――――Slave

    I understand that it can not be normal operation by the previous E2E exchange.(e2e.ti.com/.../669847
    In the case of VCCA>VCCB, it is stated that it will not be able to satisfy the electric characteristics.

    "My recommendation is to just make sure VccB stays above 2.7V (datasheet spec) and be aware when
    VccA goes above VccB the device is no longer following recommended settings and may not meet datasheet spec.
    Small voltage deviations likely won't damage this device."

    Is my understanding wrong?

    Sorry for asking so many questions.

    Best Regards,
    Ishiwata

  • Hey Ishiwata-san,

    So the e2e post you are referencing was before I found out we tested the device for VccA>VccB.

    I found out later that testing showed the device was functional when VccA>VccB. I do think I should point out if VccA is much larger than VccB then the ViL on A side will no longer meet datasheet spec of 30% of VccA. In the worst cases according to the test reports ViL on A side was as low as 0.25*VccA.

    In your case, your Vcc here is 5V so at worst case, your ViLc would be 1.25V which would still allow for communication on I2C.

    "Is my understanding wrong?"
    So there are two things here. One is does the device work? And two: Does it meet datasheet spec?

    #1 The device will still function, where you will be able to transmit a low from A side to B side and B side to A side no problem.

    #2 The prop delays and ViL on A side MAY not meet our datasheet spec anymore

    So if you are okay with not being able to meet datasheet spec BUT are able to use the device functionally then using TCA9517 in your application will be fine.

    "Sorry for asking so many questions."
    This is fine. The e2e forum is a place where we expect to ask and answer questions. No need to apologize.

    Thanks,
    -Bobby
  • Hi Bobby

    Thank you for your great support.
    I understood.

    Best Regards,
    Ishiwata