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TCA9545A: Vih max definition

Max Wu
Prodigy 30 points
Part Number: TCA9545A

Hi Sir:

I am very confuse about Vih max in datasheet 6.3 Recommended Operating Conditions describe.

according to table 6.3  appear that Vih is 0.7Vcc~ Vcc+0.5.

Now my question is that my circuitry is connect  VCC of TCA9545A Vcc to  power rail 2.5V.

function pin A1 and INT3~INT0 pull to VCC 3.3V via resistor.

Here the Vih 3.3V> (2.5V+0.5V) and exceed max requirement.

it was very interesting why Vih is refer to Vcc+0.5 v not 6V.

Are there side any about my design?

Thanks,

  • 0
    TI__Mastermind 47948 points

    Hi Max,

    The reasoning for the max voltage value on VIH being VCC+0.5V is that we don't want to reach the reverse breakdown voltage of the ESD diode on the VCC pin. Considering your application where you have VIH = 3.3V > (2.5V +0.5V) would mean you are exceeding datasheet limits, and also creating a voltage differential that is supplying the VCC pin with back current. If you want to keep your VIH at 3.3V, you would need to increase your supply voltage VCC to match recommended operating conditions. 

    Also in your application, you should connect the address pins directly to ground or VCC. No pull-up required. Pullups are required on the INT pins, which you have correct. 

    Regards,

    -Tyler

  • 0 in reply to Tyler Townsend
    Prodigy 30 points

    Hi Tyler:

    I am still not 100% clear about Vih( max) large than operating voltage will cause reverse breakdown voltage of the ESD diode on the VCC pin.

    Another question is in pin RESET.

    Base on datasheet of TCA9545A where shows Operating power supply voltage range of 1.65 V to 5.5 V and All I/O terminals are 5.5 V tolerant.

    the criteria of the pin RESET which Vih max also define as VCC+0.5V ,why the condition is not same as SCL/SDA ?

    Thanks,

  • 0 in reply to Max Wu
    TI__Guru 73541 points

    Hi Max,

    We haven't had any reported issues of the input pins backbiasing on these devices. If I had to guess, it's because one of the prior devices which was used as the building block for this device had an issue with the backbiasing of an ESD diode (I recall the TCA64xx non A family had this issue). My other guess is we may have spec'd it like this inorder for us to meet electrical characteristics better as biasing above the Vcc level may have affects on the supply current measurements.

    By technicality, we can't tell you that we are okay with you leaving your design like this since it's operating outside of recommended operating conditions but what I can do is reach out to the design team to verify if we have any concern for backbiasing of any ESD cells on the input pins.  

    -Bobby