PCA9518: I2C HUB functionality clarification

A V Meiyappan

Part Number: PCA9518

Hi,

We are using PCA9518 I2C HUB in our design and using all 4 lines (SCL/SDA 1-4) most of the times.

In one of the case, we are not using SCL/SDA-3 line and left at high impedance state. At this scenario even though all the other 3(SCL/SDA 1,2 & 4) lines are connected, it is not working as expected i.e., not able to read/write properly.

But if we pull up SCL/SDA-3 lines, then all the other lines are working as expected.

In the datasheet it is mentioned that "Powered-Off High-Impedance I2C Pins". If this is the case, ideally even if one of the l2C line is in high-impedance it should be cut off and the other 3 lines should work as expected. But in the actual scenario if one of the line is in high-impedance state other lines are not working as expected.

This means we should pull up all the I2C lines if it is unused?

Thanks,

A V Meiyappan

over 5 years ago

0 Miguel Robertson over 5 years ago

TI__Guru 62920 points

Hello,

Figure 3 in the datasheet does show unused channels being pulled high, so I would follow that recommendation. Out of curiosity, though, how are you configuring the enable lines?

Max

0 A V Meiyappan over 5 years ago in reply to Miguel Robertson

Prodigy 40 points

Hi Max,

Thanks for the clarification. We are using external PU/PD to configure the enable lines.

Regards,

A V Meiyappan

0 Miguel Robertson over 5 years ago in reply to A V Meiyappan

TI__Guru 62920 points

Got it. I still believe pull-up resistances on Ch. 3 should solve the issue, then. If you have a way to pull EN3 low when Ch. 3 is not in use that could be a solution as well.

Regards,
Max

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PCA9518: I2C HUB functionality clarification