PCA9548A: I2C signal random fail in communication!!

Paul Yeh

Genius 16215 points

Part Number: PCA9548A
Other Parts Discussed in Thread: TCA9548A

Hi Team,

Customer highlight our PCA9548A cause their I2C communication fail and need our suggestion to debug this issue.

They use 4 channel to read different sensor devices and read one device repeatedly but sometimes it is fail in reading.

But after they reset our device then I2C commination will resume to normal.

So they think this issue is related ours.

I attached files for team for checking possible reason.

Customer's data

https://drive.google.com/drive/folders/180Q3zheM6A9VPEnBLG_Dr8WxEeb92qt2?usp=sharing

LA LOG tool

Logic+Setup+2.3.47-master.exe

LA record file

Session 5.sal

The general circuit is in below, Host side pull up voltage is 3.3V, our IC's VCC is also 3.3V.

As for slave side pull up voltage is 1.8V.

Thanks

over 3 years ago

0 Paul Yeh over 3 years ago

TI__Genius 16215 points

TI Drive

https://tidrive.itg.ti.com/a/eWjKd_LoynJraMp0/46357ea6-307d-4a94-a89f-696aeeabcdfb?l

Thanks

0 Paul Yeh over 3 years ago in reply to Paul Yeh

TI__Genius 16215 points

Hi team,

Just upload customer's real circuit for you.

Thanks

0 Clemens Ladisch over 3 years ago in reply to Paul Yeh

Guru 317280 points

As explained in section 9.2.1 of the datasheet, a supply voltage of 3.3 V is too high for 1.8 V signals.

If the problem is related to voltage levels, then an oscilloscope trace would be helpful.

0 Chris Ayoub over 3 years ago in reply to Clemens Ladisch

TI__Genius 15345 points

Hi Paul,

Is the device able to communicate at all or is it constantly NACK-ing? As Clemens said this device has a restriction on what the VCC voltage can be:

Using the graph above you must set the VCC voltage so that the corresponding VPASS voltage is lower or equal to the lowest bus voltage on the device. When VCC = 3.3V your VPASS is around 2V which is too high. An easy way to fix this for your set up is to set VCC = 1.8V and connect it to the same rail that your other I2C buses are using. Since this device isn't defined to use 1.8V I would recommend upgrading to the TCA9548A. However, due to the crazy supply chain issues you should be able to get away with running the PCA9548A at 1.8V but we do not guarantee that it will work.

Best,

Chris

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PCA9548A: I2C signal random fail in communication!!