TCA9555: TCA9555 Schematic review

Smith,

Thanks for reaching out! I had the opportunity to take a look at the file you provided. I have feedback for the implementation of the TCA9555.

For unused ports P13-P17, if they will be left unconnected, you should set these ports as outputs in order to prevent significant current consumption by floating input stages. Alternatively, these could be left as inputs and tied to either VCC_IO or GND.

I cannot tell specifically what LEDs are being used in this design for LED1-LED12. If these have low current consumption (i.e. <10 mA when on) then these should likely be fine. If they are higher, you should ensure that you are not violating any of the overall current consumption or power dissipation requirements of the TCA9555. While individual IO pins of the TCA9555 are capable of sinking 25 mA, the device would not be able to sink 25 mA across all pins. The Absolute Maximum Rating for the continuous current through GND is -250 mA. I recommend looking at section 10.2.2.1 of the TCA9555 datasheet, which shows a detailed procedure for calculating junction temperature and power dissipation, which would guide the maximum use case if your LEDs consume higher current and multiple will be active at a time. I believe I read in point 4 of the note on the schematic that all of the LEDs will turn on when BAT is full. Please check to ensure the power dissipation and junction temperature requirements of the device will be met.

On the schematic, it looks like the IO_INT net is labeled as an input to the TCA9555. Please note that INT is an open-drain output, not an input. This input is triggered when a rising or falling edge of any input pin is detected. This allows the device to notify the microcontroller of changes to input pins without the microcontroller needing to continuously check the input stages. See section 9.3.3 of the datasheet for more information on the INT output.

Please let me know if you have any more questions!

Best,

Danny