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[ TCA9517 ] Requirements for Level Translating Application

Kenichiro
Mastermind 9165 points
Other Parts Discussed in Thread: TCA9517, TCA9517A, TCA4311A

[ TCA9517 ] Requirements for Level Translating Application

Hi,

My customer has been working on the project for few years which uses multiple TCA9517s for their I2C level translation block. According to latest datasheet, new ”Design Requirements” added, and it must be met “Vcca < Vccb”.

 

Q1: Can you elaborate why this requirements added from latest datasheet?

 Since previous datasheet does not have this kind of requirements, so their design already has some blocks that do not meet with “Vcca < Vccb” requirement, they have to modify their schematics.

 

 Q2: According to customer experience, it can be seen that the level translating function with Vcca > Vccb (not meet with requirement) is more sensitive to noise from adjacent function block. (the block with Vcca < Vccb is less sensitive.)

Does this make sense? Can you explain how this difference on noise performance caused? 

 

Q3: The changes only on datasheet, TI has NOT changed anything of TCA9517 itself. Correct?

 (We, disti in Japan, have received PCN which is related to adding fab and wire material changes)

Thank you for your support on this matter in advance.

Regards,

Ken

  • 0
    TI__Genius 16430 points
    Ken-san,
    To answer your questions:
    1) This requirement should have been in the datasheet since the first revision, however it was not very explicit and clear. In a recent update, we added a new application section which has design requirements (to conform with TI's latest datasheet requirements), and we made these requirements more explicit. Please keep in mind that 2 B sides of the device cannot be connected together (you CANNOT go ------A-(TCA9517)-B ------------ B-(TCA9517)-A ------).

    2) This is part of the reason why we decided to make this requirement more explicit. While, it will function, the thing is that the B side of the device has a static voltage offset of about 0.5 V. So if VCCB is lower than VCCA, that 0.5V will provide for less noise margin at lower voltages. The device will still function, but you may see some issues from reduced noise margins, such as false clock edges)

    3) You are correct, the die of the TCA9517 has not changed at all. Purely a datasheet change.
  • 0 in reply to Jonathan Valdez
    Mastermind 9165 points
    Hi Jonathan,

    Sorry that I did not reply to you.
    I have checked old datasheet, but for me it was not clear that there are some restrictions. Anyway, now we have clear description for future engineer! Thank you.

    Here is the another good reference for this discussion.

    TCA4311A, TCA9517, TCA9517A - some questions
    e2e.ti.com/.../447225

    Thanks,
    Ken