PCA9554: PCA9554PWR

Carlos Lizandro

Part Number: PCA9554
Other Parts Discussed in Thread: TCA9554, , TCA9554A

Tool/software:

Hello everyone. Not sure if this is the correct place to ask this question but I would like to know if I can add external pulls, 10k Ohms to the P[n] ports of the PCA9554. My understanding is that they are configured by default as inputs and that as such, they have weak pull ups inside already (100K). If I want the I2C line to read a logic 1, can I just leave the P[n] pin floating or do I need an external pull up that I can assign any value to it (right now, I am using 10k Ohms)?

I know that if I want the I2C bus to ready a logic 0, I'll need to add a zero ohms pull down resistor.

Thanks you all very kindly

Carlos Lizandro

over 1 year ago

0 Tyler Townsend over 1 year ago

TI__Mastermind 49968 points

Hi Carlos,

This is the right place to ask these types of questions.

Adding external pull-ups (10k) is not required for PCA9554 due to internal 100kohm pull-up resistance. If you want a stronger pull-up, you can certainly add one in parallel to the internal 100k externally.

Upon power up, PCA9554 will have its IO's configured in the INPUT mode. Therefore, due to 100k, the input will read a logic HIGH if the P[n] pin is left floating.

You are correct if you want a P[n] pin to read logic LOW, you will need some type of external pull-down resistance that can bring the voltage down on that pin past a VIL (input logic low voltage).

0 ohms would work here, or even something like a 1kohm (much stronger than 100k).

Regards,

Tyler

0 Tyler Townsend over 1 year ago

TI__Mastermind 49968 points

I forgot this in my response just now. Please try moving to the TCA9554. This device is more robust, uses newer process technology, has wider voltage range, can run up to 400kHz, and fixes any errata present in the PCA9554. TCA9554 is p2p (pin to pin) compatible to the PCA9554.

0 Carlos Lizandro over 1 year ago

Prodigy 20 points

Tyler. Thank you so kindly for responding and answering my questions. I have followed your advice and incorporated the TCA9554 in my schematic. Please consider this case closed.

Carlos Lizandro

0 Carlos Lizandro over 1 year ago in reply to Tyler Townsend

Prodigy 20 points

Tyler, I am just finding out that there is a small difference between the PCA and the TCA and that is in the slave address. On the fixed bits, the PCA is configured as 0100 and in the TCA 0111. No big deal but thought I should bring it up.

Carlos Lizandro