Intersil introduced the ISL88694. A dual active pull-up bus terminator, the ISL88694 is designed to improve data transmission speed and reliability on SMBus or similar 2-wire serial bus interfaces such as I2C. It permits operation of the bus at frequencies of up to 100 kHz despite the capacitive loads of multiple devices and/or long PC board traces.
Pull-up resistors are typically used to connect each bus line to a positive supply voltage such that both clock and data lines are high when the bus is free. However, using simple pull-up resistors on the clock and data lines becomes problematic if there are long signal lines or many devices connected to the bus. In such cases, the combined capacitance of the bus then increases the rise time on the signal to such an extent that bus communication becomes unreliable or fails to meet the bus timing specifications.
To improve the operation of a 2-wire bus where larger bus capacitance exists, the ISL88694 provides active pull-up using switched current sources. When the bus line is released, it is pulled high by the ISL88694 active current until the voltage exceeds a given threshold for a period of time. This voltage-time combination filters out noise on the signal line. If both inputs are high, the pull-up current drops to the standby level of 100 µA to minimize power consumption.
In addition to improving bus transmission speed and reliability, the ISL88694 also provides active termination for bus lines. A noise filter on each channel prevents the device from responding to input transitions below a voltage-time threshold.
