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TCA9517 - Power supply requirement VCCA < VCCB

Kawai
Guru 19785 points
Other Parts Discussed in Thread: TCA9517

Hi Team,

I have a question about TCA9517 power supply requirement VCCA < VCCB which listed in the datasheet.

[Question]
Please advise us if user could use TCA9517 in the condition of VCCA > VCCB.

I've found some information in the following post.

https://e2e.ti.com/support/interface/i2c/f/390/p/266001/933222#933222

> The TCA9517 is powered off of the VCCB rail and the VCCA rail is just used as a reference level for the A inputs.
> This is why we always recommend that VCCB (main supply voltage) is higher than the VCCA side.

From this post, I understood that VCCA is only used as a reference level and VCCB is the power for the IC. In this case, I think VCCA < VCCB is not a must power requirement. I believe the device could be used as long as VCCB is higher than 2.7V.

Datasheet "Recommended Operating Conditions" does not show VCCB to be higher than VCCA.

Best Regards,
Kawai

  • 0
    TI__Genius 16510 points
    Kawai-san,

    As previously mentioned in the thread that you found, VCCB should always be greater than or equal to VCCA. While Chris is correct that the device is powered off of the VCCB rail internally, the issue is that when VCCA > VCCB, there can be internal underdrive issues in the translation logic, where some signals may not be properly interpreted as a logic low or high (internally), causing communication failure.

    At higher voltages for VCCA and VCCB, it technically will work, but we do not guarantee the electrical specifications in the datasheet for that operation.
  • 0 in reply to Jonathan Valdez
    Guru 19785 points
    Hi Jonathan-san,

    I understand. Thank you very much for the detail explanation.

    Best Regards,
    Kawai