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TCA9539-Q1: the relationship between RESET and INT pin

Sherry Liang
Genius 10255 points
Part Number: TCA9539-Q1

Dear team,

We don't plan to use RESET pin, so we connect this pin to VSYS_3V3 with a pullup resistor. But we found that INT pin is always low when RESET connect to VSYS. 

in addition, VCC connects to VSYS_3V3, and this power is always high after power on, which means we don't perform power on reset operation. Is the power-on-reset necessary?

Thanks & Best Regards,

Sherry

  • 0
    TI__Genius 15345 points

    Hi Sherry,

    Why is there a voltage divider on the INT pin? Is it because the microcontroller requires a 1.8V input? If that is the case you can just pull up the INT pin to 1.8V if that is what the microcontroller is being powered with. It does not need to be pulled up to VSYS_3.3 it is just an open drain output.

    The INT port can be activated for a couple different reason. The first is if there is any rising or falling edge on the input ports. The second is if there is a change of the I/Os after resetting. The RESET pin really has no affect on the INT pin. 

    How were you able to verify that the INT pin is always low when RESET is connected to VSYS? Did you connect RESET to another 3.3V source, did you remove the pull up on the RESET pin? A power on reset or a reset of any kind is not necessary to get the INT pin to work.

    I would check to see if you could clear the interrupt pin. You would have to read data from the port that generated the interrupt. In your case since we are unsure which port generated the interrupt I would just read every port on the device and see if the INT is cleared.

    Best,

    Chris

  • 0 in reply to Chris Ayoub
    TI__Genius 10255 points

    Hi Chris,

    1. Yes, the customer reads two input ports, and the INT signal is cleared and become high from low. 

    2. Currently reset pin connects to VSYS, when the customer shorts this pin to GND with tweezers, the INT pin will become high from low.

    3. When the customer simulates POR with VCC which means that set VCC=VSYS firstly, then set VCC=0, finally set VCC=VSYS, the INT pin will become high from low.

    My question is as below,

    1. Is the power-on reset necessary when powering on?

    2. In the block diagram, INT circuit has no relation with the RESET pin or POR, but INT status will change when give RESET pin a low signal or execute POR. Could you please help analyze this?

    Thanks & Best Regards,

    Sherry

  • +1 in reply to Sherry Liang
    TI__Genius 15345 points

    Hi Sherry,

    Sherry Liang said:
    1. Is the power-on reset necessary when powering on?

    A POR is not necessary when powering on, in-fact pulling the RESET pin low does the same this as a POR. All this does is set the I/O ports back to their default values.

    Sherry Liang said:
    2. In the block diagram, INT circuit has no relation with the RESET pin or POR, but INT status will change when give RESET pin a low signal or execute POR. Could you please help analyze this?

    The reason this happens is because the INT pin will go high when an input port has it's value changed from it's original value. If after a RESET the input ports return to their original values then this would make the INT pin go high.

    To continue to debug this issue, now that we know that INT pin can be cleared it is most likely an issue with your input ports. Do all input ports on the device have a pull-up/pull down resistor? All input ports must be referenced to either GND or VCC. if they are left floating the device will be unsure how to read them as HIGH or LOW so that could make your INT go high.

    Best,

    Chris