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TCA9517 - VCCA, VCCB Requirement

Kawai
Guru 19775 points
Other Parts Discussed in Thread: TCA9517

Hello Team,

There is "design requirement" description "VCCA < VCCB" in the TCA9517 datasheet, as follows.

[Q1]
I believe this should be VCCA <= VCCB. Is my recognition correct ? There would be an application without level shifting, VCCA = VCCB.

[Q2]
In the case of VCCA and VCCB is 3.3V but different power source, voltage relation could be VCCA > VCCB for a few tens of mV. Can you accept such use case ? What is the criteria that the device could not be used ?


Best Regards,

Kawai

  • 0
    TI__Expert 5140 points
    Hi Kawai-san,

    Thank you for the question.

    I will explain the voltage differences for VCCA and VCCB to give more perspective

    - VCCA = VCCB should work with no issue
    - VCCA < VCCB is recommended due to VCCB having a static voltage offset
    - If by chance VCCA were to exceed VCCB in voltage, the device will still function properly, but the voltage offset will be a larger percentage of VILmax of the slave. This cannot guarantee operation within the specifications. As long as the IOL into the device is less than or equal to 6mA, we can guarantee the VOL will not be above the spec maximum.

    Thanks,
    Siby
  • 0 in reply to Siby James
    Guru 19775 points
    Hello Siby-san,

    Thank you for the information. I am not clear about the following portion. Could you please explain in more detail ? How come does the offset, which I believe V_ILC, comes larger when VCCA > VCCB ?

    > but the voltage offset will be a larger percentage of VILmax of the slave. This cannot guarantee operation within the specifications.

    Best Regards,
    Kawai
  • 0 in reply to Kawai
    TI__Expert 5140 points
    Hi Kawai-san,

    What I mean is that there is a direct relationship between the increase in VCCA > VCCB to the offset voltage. As this approaches VILmax, this cannot guarantee operation as it will be out of spec. Hence, why we tend to use IOL for this use case to ensure we won't be above VOL.

    Thanks,
    Siby