Expert Opinion - Query 1

What is EOL in I2C bus and how to calculate that register value for bus termination?

Reply 1:

If i understand correctly, your question talks about the termination of the i2c bus with multiple devices on the line. EOL must be end of the line. When you talk about setting the register, it might be for calculating the signal delay for achieving the synchronization.

Reply 2:

The thing is when we add resistance in bus also we need to look at once bus capacitance for multi devices. Also it will say how much your bus length to communicate with devices

Reply 3:

Bus length we might now because it is the trace length layed out. I am worried how you arrive at trace capacitance. Leaving capacitance at load and source, bus capacitance is always an assumption

Reply 4:

Yes.. generally 4.7k works if devices on same board (may be max 3).. if board to board then go with 1k or less.. you need check the rise time and modify the resistance.. don't put too much lower value because power consumption will be more..

Reply 5:

I guess board to board is not feasible in I2C.. If you are talking about mother and daughter board scenario, then it works.. Modifying the resistance with rise time measurement is the best option but in real time it is less implemented unless you see an issue in I2C communication

Reply 6:

Capacitance can be estimated based on number of devices and load cap typical value from data sheet of each device.

Reply 7:

In Reply 3, By source and load i meant datasheet value only.. The only assumption here is the trace capacitance

Reply 8:

In reply to 5 above, I would also suggest to fine tune this by measuring few para on oscilloscope with actual pcba in hand... e.g. rise time fall time n overshoot

Reply 9:

I guess  pcb tool can give trace cap estimates... is it possible?

Reply 10:

We used to calculate with a customized excel sheet.. Never did that through layout tool.. Some layout engineer should give their opinion if they have done before

Reply 11:

Most layout tools do have capability to estimate Impedance and propagation delay but not capacitance... For capacitance some SI tools can give better estimate...