PCA9615 noise power supply

[yannick_bfp]

Hello,

I want to use PCA9615 because I have a lenght cable about 2 meter between my master and the I2C slave.

I have buy the kit sparkfun with PCA9615 and I try it with ethernet cable between the both.

This's don't work. My power supply is very noise. I see the SCL/SDA on the master side, but I see only on DSDA- and DSCL- signal. There's nothing on DSDA+ and DSCL+, and so nothong on the slave side.

Does the power noise can be the problem ? Or what ?

I'm not sure this's the best IC choise. I see also the PCA9605.

Best regards

[yannick_bfp]

Hello,

Can I use PCA9511A for my application ?

I have about 2 meters length of I2C and the slave side is disconnectable. 

But I have noise on the power supply, on the slave side.

Does I need to use 2 PCA9511A, one on each side master and slave ?

Best regards. 

[lisettelozano]

Hello,

The PCA9511A can work if your application implies to disconnect and connect a card. Also, the PCA9511A can be used as a repeater/bus extender application (for long cables).

And yes, you will need to use two devices, one at each extreme of the cable.

I recommend you to check the application note AN255 page 19; it will provide more information about both configurations https://www.nxp.com/docs/en/application-note/AN255.pdf

Have a great day,

Paulina

[yannick_bfp]

Hello,

I try 2 PCA9511A. On the slave side, I have 2 I2C Slaves, and sometimes (about 1/20), the second slave don't answer. Does I have to put 2 PCA9511 on the slave side, one for each slave ? I don't think.

I try also 2 PCA9512A with shift level at 5V. It's the same result, sometimes the second slave don't answer.
What do you think I can do ?

Best regard

[lisettelozano]

Hello, 

First, please accept my apologies for the delayed response. 

Do you still present the issue? Have you tried by using two PCA9511A on the slave side? 

Have a great day, 

Paulina

[yannick_bfp]

Hello,

Yes I resolve my problem. Finally, I use P82B96 and it work fine.

Best regards

[lisettelozano]

Hello,

Yes, the noise in your power supply can be an issue. The PCA9615 is a differential I2C-bus which is targeted for long I2C-bus runs in electrically noisy environments. The usage of this IC with the proper termination resistor network can help with the issue. Please refer to the sections 7.2, 7.3 and 8.2 from the datasheet https://www.nxp.com/docs/en/data-sheet/PCA9615.pdf

Also, we recommend the OM13523UL demo board which can help to evaluate the differential I2C-bus (dI2C-bus) such as the PCA9615, the PCA9614 and PCA9616.

We also have the P82B715 which is an I2C-bus extender which allows to drive I2C-bus signal over long cables to approximately 50 meters or increase the total connected capacitance to around 3000 pF (normal I2C-bus capacitance limit of 400 pF).

I hope this information can be helpful. Please let me know if you have further questions.

Have a great day,

Paulina

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