TMAG5273: Multiple devices on the same I2C line

Hello Piotr,

Thanks for posting to the sensors forum!

Are you adding pullups to every single I2C line? Or are do you only have one set of pullups for the entire I2C bus? If you have multiple pullups the load will become to large to drive the signal appropriately so only one set of pullups resistors are required.

Assuming you are only using one set of pullups the other issue could be your supply, are you using your microcontroller power supply to pull up the SDA and SCL lines on the TMAG5273? If this is the case, the current load demand may be too large for your microcontroller source, you may try to change the pullup value to see if this helps but for 16 devices you might require a separate supply.

Have you tried using a separate supply to pull up the I2C lines on your devices to see if this makes a difference? 

Best,

Isaac

Hello,

We are using same schematic as in datasheet:

I2C has 2.2k pullups to 3.3V from nucleo board which has 0.5A LDO, so there is no problem with power supply.

I have to change my previous issue description.
On the prototyping board we have four TMAG5273 devices.
All devices are connected to I2C bus.
When all devices have connected power supply then voltage on I2C lines are 3.3V, transmission on adress 0x00 works but of course all devices are answering on the same time so data are corrupted.
When only single device has connected Vcc, then voltage on the I2C bus is ~2V and sometimes even lower.

The devices are probably trying to get power from I2C lines and that's why there is this voltage drop described above.

We can't use Address Expansion feature described in chapter 8.2.2 of datasheet. It just doesn't work.