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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.
Which is 2 channel pin selectable I2C multiplexer?
The LTC4312 and LTC4314 pin-selectable 2-channel and 4-channel I 2 C multiplexers with bus buffers address these issues with a number of powerful features (see Table 1). Since these two devices share the same features, except for the number of channels, this article focuses on the LTC4314.
When do pull up resistors pull the line high?
The pullup resistors pull the line high when it is not driven low by the open-drain interface. The value of the pullup resistor is an important design consideration for I2C systems as an incorrect value can lead to signal loss.
Why are I2C and SMBus protocols so popular?
The inherent simplicity of I 2 C and SMBus 2-wire protocols has made them a popular choice for communicating vital information in large systems. Both standards employ simple open-drain pull-down drivers with resistive or current source pull-ups. Nevertheless, several practical problems arise as systems grow in complexity.
What is the required sink current for I2C?
When all the pullup resistors are combined, the required sink current can be calculated. The maximum is 3 mA to meet the i2c specifications. To compensate for wire capacitance the i2c bus speed can be lowered.
What’s the maximum capacitance of an I2C resistor?
The maximum of all the capacitances are limited to 400pF by I2C standard, and you’d have to have either a really long signal trace on your PCB or a lot of devices on it to get anywhere near 400pF, but as the frequency of your signal increases, the impact of that charging rate will have a dramatic affect.
What is the I2C bus and what does it do?
The I2C bus is a standard bidirectional interface that uses a controller, known as the master, to communicate with slave devices. A slave may not transmit data unless it has been addressed by the master. Each device on the I2C bus has a specific device address to differentiate between other devices that are on the same I2C bus.
How to calculate the maximum pull up resistance?
This is the final form to use in calculations for the maximum pull-up resistance; t Rise Time, V Logic Low, and V Logic High are given in the datasheet, and C Bus is estimated based on the characteristics of your circuit.
What are the start and stop conditions of I2C?
2.1.1 START and STOP Conditions. I2C communication with this device is initiated by the master sending a START condition and terminated by the master sending a STOP condition. A high-to-low transition on the SDA line while the SCL is high defines a START condition.