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TCA6424A: any leakage current if I/O pin voltage (5V pull up) > Vcc (3.3V)

Alan Chang
Intellectual 2320 points
Part Number: TCA6424A

Hi,

   A question about TCA6424A IO pin voltage, if 5V rail on I/O pins as pull-up, but 3.3V is used on both Vcc and Vccp pins. will it have leakage current to Vcc and Vccp pins from 5V at I/O pins?

  this statement on data sheet, not sure what meaning of " should not exceed the recommended level" .

If the I/O is configured as an output, Q1 or Q2 is enabled, depending on the state of the output port register. In
this case, there are low-impedance paths between the I/O pin and either VCC or GND. The external voltage
applied to this I/O pin should not exceed the recommended levels for proper operation.

  • 0
    TI__Mastermind 48338 points

    Hi Alan,

    Alan Chang said:
       A question about TCA6424A IO pin voltage, if 5V rail on I/O pins as pull-up, but 3.3V is used on both Vcc and Vccp pins. will it have leakage current to Vcc and Vccp pins from 5V at I/O pins?

    I believe this is dependent on the configuration and state of the IO pin whether output or input. If the p-port is used as an input, I don't necessarily see a problem with this since inputs are high-z. 

    I do think it is possible to have a leakage path when the IO pin is configured as an output. If outputting a logic LOW, I don't see an issue, as current will flow from the 5V source through the pull-up resistor, through the small RDS_ON of Q2 to GND. This is okay, because Q1 is high-z. 

    I think the problem occurs when Q1 is turned ON (push-pull amplifier is outputting VCCP). Then this would create a path from the 5V source through the pull-up resistor through the RDS_ON of Q1 to VCCP, back-biasing the supply since it is of lower potential. 

    Alan Chang said:
      this statement on data sheet, not sure what meaning of " should not exceed the recommended level" .

    The statement "recommended level" is usually found in the recommended operating conditions of the datasheet which I have listed below.

    Generally speaking, if the recommend operating conditions are followed, you can expect the device to behave according to the electrical specifications in the datasheet. If you traverse outside the recommended operating conditions, the device may not be properly or show certain electrical characteristics as listed in the datasheet. However, the absolute maximum conditions always need to be respected at all times in order to ensure permanent damage is not done to the device. 

    Regards,

    Tyler