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TCA6424A: how to guarantee I/os are low on startup

Dan Andersen
Genius 11390 points
Part Number: TCA6424A

For TCA6424ARGJR, if we want to make sure the default state of a port is low before any software configure the port, we put a pull down resistor to do this correct?

What is the recommended pull down resistor to insure this?

Also, if the /RESET pin is held low will the ports be HiZ, or in a known state?  The datasheet timing diagram makes it appear this happens after reset is released....

 

For our application, we only use this for output, none will be used as input.

 

Regards,

Dan

  • 0
    TI__Guru 62920 points
    Hi Dan,

    Yes, a pull-down resistor would be the best solution to keep the I/O ports at a low level while they are configured as inputs (i.e., the default start-up state). In input mode the leakage current into the P ports will be small (<1 uA), and so even relatively large resistor values will be suitable to maintain a voltage that is close to ground. Something like 10 kOhm would be a reasonable value to maintain a low level in input mode without dissipating a lot of power when the device is outputting a high level on these ports.

    The internal registers are reset shortly following a falling edge on /RESET, and once this occurs the P ports will be configured as high-Z inputs.

    Please just let me know if you have any further questions.

    Regards,
    Max