Contents
How to calculate the capacitance of an I2C bus?
To calculate the bus capacitance simply add up all the area of the traces, the distance to ground and the dielectric and calculate away. So yes it is not simple to do. 2. It is in the i2c spec. 127 minus the reserved addresses.
Why is copper trace capacitance important in I2C?
Copper Trace Capacitance When we say “copper trace capacitance” here, we’re referring to single trace over dielectric over ground. The capacitive coupling between the I 2 C signal lines and the ground plane can be significant if the ICs are far from each other, or multiple ICs are on the I 2 C bus.
Why does accuracy not matter in the I2C bus?
The I2C Clock Speed – Why Accuracy Doesn’t Matter. In a synchronous serial transmission like an RS232 communication the clock speed is predetermined. Since the receiver does not get an explicit clock signal it has to rely on the accuracy of the sender’s timing. Any deviation is almost fatal as it may cause errors sooner or later.
Where do I find the capacitance of the bus?
The bus capacitance includes not only the capacitance between each signal line (clock and data) to return, it includes the input capacitance of each device attached to the bus. This input capacitance can usually be found in a device’s data sheet.
What’s the minimum clock speed for an I2C device?
Note that I2C devices don’t have to sink more than 3 mA, therefore at 3.3 V the bus capacitance shouldn’t be higher than about 395 pF, otherwise the pull-up resistance would have to be smaller than 1100 Ω, and allow more than the 3 mA. That’s the greenish dashed lines.
How many devices can you put on an I2C bus?
As a practical matter, one can put up to about 10 devices on an I2C bus without too much problem. Trying to put 30 devices becomes very difficult due to the capacitance. Another issue is that a lot of devices generally means a long bus (more than about 20-25) cm and a long bus often has problems with noise pickup.
Why is capacitive coupling important in the I 2 C Bus?
The capacitive coupling between the I 2 C signal lines and the ground plane can be significant if the ICs are far from each other, or multiple ICs are on the I 2 C bus.