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How do you find the pull-up resistor value for I2C?
Each signal line has a pull-up resistor on it, to restore the signal to high when no device is asserting it low. Notice the two pull-up resistors on the two communication lines. Resistor selection varies with devices on the bus, but a good rule of thumb is to start with 4.7kΩ resistor and adjust down if necessary.
What is the use of pull-up resistor?
In electronic logic circuits, a pull-up resistor or pull-down resistor is a resistor used to ensure a known state for a signal. It is typically used in combination with components such as switches and transistors, which physically interrupt the connection of subsequent components to ground or to VCC.
What is use of pull up resistor?
In electronic logic circuits, a pull-up resistor or pull-down resistor is a resistor used to ensure a known state for a signal. A pull-up resistor effectively establishes an additional loop over the critical components, ensuring that the voltage is well-defined even when the switch is open.
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.
How is the pull up resistor of an I2C bus limited?
The maximum pullup resistance is limited by the bus capacitance (Cb) due to I2C standard rise time specifications. If the pullup resistor value is too high, the I2C line may not rise to a logical high before it is pulled low.
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.
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.