PCA9539 - unused I/O ports

Kawai

Guru 19785 points

Other Parts Discussed in Thread: TCA9539

Hi, could you please tell me what to do with the unused I/O p-ports ?

I believe that they should be pulled down or up to keep logic low or logic high.

Our customer uses this device leaving the unused port open.

If they assign the port as an output, could they leave the port open ?

I am worrying the behavior of the device which the I/Os are configured as input when at power-up.

Thanks and Best Regards,

Kawai

over 12 years ago

0 Kawai over 12 years ago

Guru 19785 points

I understand that the device is NRND, but could anybody help us with this question ?

The same thing could be said to the new part TCA9539, too.

Best Regards,

Kawai

0 Andrew_Mason over 12 years ago in reply to Kawai

TI__Expert 6395 points

Hello Kawai,

The best action would be to leave the unused ports as inputs and tie them to GND. As a floating node after power up, the input could toggle repeatedly which will cause interrupts and increase ICC due to the nature of CMOS inputs.

If the customer is okay with the above then there are no issues.

Regards,

Andrew

0 Kawai over 12 years ago in reply to Andrew_Mason

Guru 19785 points

Andrew-san,

We appreciate for your reply.

Do you mean, interrupts and ICC increase would(may) occur during the time range from Power-up to Register Programming ? (Until the port set to output?)

Best Regards,

Kawai

0 Andrew_Mason over 12 years ago in reply to Kawai

TI__Expert 6395 points

Hello Kawai,

Because the input pins are floating, they may be toggling repeatedly before the pins are set to outputs. I was referring to the interrupt created by this condition that is detailed on page 10 of the datasheet.

Regards,

Andrew

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PCA9539 - unused I/O ports