TCA9555: What is the I/O pin logic status when it powered on

Xiaosong Shi

Part Number: TCA9555

Hi,

I am using TCA9555 to drive some relay drivers, and like to know the I/O output status when it just powered on. The spec says the I/Os are configured as inputs, and the block diagram shows a 100K pull-up resistor to VCC. Can I assume that the I/O output status is default to high/VCC?

Thank you,

Ray

over 7 years ago

0 Miguel Robertson over 7 years ago

TI__Guru 62920 points

Hi Ray,

Yes, by default the IOs are configured as inputs and each input has a ~100-kOhm pull-up resistance which will establish a default-high state as long as external devices do not sink enough current to pull the voltage low.

Max

0 Xiaosong Shi over 7 years ago in reply to Miguel Robertson

Prodigy 30 points

Hi Max,
Thank you for the information.
Since the I/O is open drain, I am assuming that I cannot use TCA9555 to drive a 1mA external device if a 10k push-down resistor is used to pull voltage low? Do you know any I2C GPIO chips that has default low on output?

Thanks,
Ray

0 Miguel Robertson over 7 years ago in reply to Xiaosong Shi

TI__Guru 62920 points

Ray,

The TCA9555 has push-pull outputs, and the recommended maximum output high-state current is 10 mA. This means it should have no problem overcoming an external 10-kOhm pull-down resistance. Use of a pull-down would be a good way to ensure a default low level when the port is configured as an input. Is that what you were asking about, or did I mis-interpret what you mean?

Max

0 Xiaosong Shi over 7 years ago in reply to Miguel Robertson

Prodigy 30 points

Max,
That's what I am looking for. Thank you very much :)

Ray

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TCA9555: What is the I/O pin logic status when it powered on