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TCA9535: TCA9535 Iq issue

Eric Shen42
Expert 2750 points
Part Number: TCA9535

Dear TI:

     The following table is the Iq parameters of TCA9535, please help to check three questions:

1,If I/O set to input, and the I/O pin float, whether I/O pin going to be unstable？

2,If I/O set to output, is the Iq unstable? Because my client test a few boards when I/O is output, and I/O all float, the Iq is all different, the minimum is 3uA, the biggest is 50uA, the TCA9535 has no CLK.

3. If I/O set to input, and I/O connect LED to GND, is there still current from I/O to LED?

     

  • 0
    TI__Guru 73221 points

    Hello Eric,

    "1,If I/O set to input, and the I/O pin float, whether I/O pin going to be unstable？"

    I am not entirely sure what you mean when you say unstable. The I/O will simply float and the device should still function though the INT pin may also toggle itself. The only issue will be that you will see more current draw because you may partially bias the CMOS gates input and see shoot through current. I would recommend you reference the pins to GND/Vcc or set the pins as an output if you want to keep your supply current lower.

    "2,If I/O set to output, is the Iq unstable? Because my client test a few boards when I/O is output, and I/O all float, the Iq is all different, the minimum is 3uA, the biggest is 50uA, the TCA9535 has no CLK."

    The supply current will be lowest when the device is set to an output. If the pins are floating inputs then the supply current could change as the floating pins drift in voltage.

    "3. If I/O set to input, and I/O connect LED to GND, is there still current from I/O to LED?"

    You are saying the pin connected to the LED will be an input? Likely in this case the LED will be turned off unless noise (from PCB or EMI) coupled onto the pin. It would be best to set the pin to an output low to make sure the LED stays off.

    Technically there will be current from I/O to the LED due to leakage but not enough to turn on the LED in most cases. When the device is set as an input, the pin is considered high impedance.

    Thanks,

    -Bobby

  • 0 in reply to BOBBY
    Expert 2750 points
    Dear Bobby:
    Thanks!
    My customer want to into standby mode, because the Iq is only 3.9uA(MAX), but the condition is I/O set to input.
    You said: "The supply current will be lowest when the device is set to an output. If the pins are floating inputs then the supply current could change as the floating pins drift in voltage."
    So when is the current minimum? Customer want into a lowest Iq status.
  • 0 in reply to Eric Shen42
    Expert 2750 points
    Hi Bobby:
    Please help to check the Iq issue.
    Thanks!
  • 0 in reply to BOBBY
    TI__Intellectual 1230 points
    Hi Bobby,

    Could you pls check the condition(input or output, floating or non-floating) to achieve lowest Iq?
    Since according to datasheet shown above, we found the standby mode would be achieved when I/O is set to input.
    Thank you.
  • 0 in reply to Lin Zhao
    TI__Guru 73221 points

    Hello Leo,

    Sorry I didn't see the messages here until just now.

    "Could you pls check the condition(input or output, floating or non-floating) to achieve lowest Iq?"

    Looking at the datasheet, the best Iq is when the device is referenced to Vcc. (Do not leave them floating). If you set the device to an output high you will reference the inputs to be seeing a logic high. Alternatively you could also just tie a pull up resistor to Vcc and leave the device an input. My thought on this is it is better to set the device as an input and supply Vcc through a large pull up resistor. (As an output high, the Ron would be low compared to an external pull up resulting in more current consumption which is why I believe using an external reference is better than using the output as reference).

    -Bobby