New Industry Products

NXP Delivers First No-Offset I2C-Bus Buffers

August 24, 2011 by Jeff Shepard

NXP Semiconductors N.V. introduced the PCA9525 and PCA9605 – described as the industry’s first no-offset I²C-bus buffers, which enable system designers to isolate capacitance and interface with other bus buffers. These bus buffers use the no-offset scoreboard method to decide signal direction, rather than using a directional pin and relying on offset voltages to control direction and prevent bus latch-up. Significantly, the no-offset devices are interoperable even with static offset or incremental bus buffers, allowing easy design-in regardless of which other devices are on the bus. In addition, NXP has introduced the PCA9646 – described as the industry’s first fully buffered 4-channel switch with no-offset ports. All devices work to 1 MHz, and the PCA9605 and PCA9646 support Fast-mode Plus (Fm+), which has 10x the normal I²C-bus drive, allowing longer I2C-buses or placement of more devices on the bus.

While I²C buses have traditionally been used in computing, consumer and portable applications where only short bus lengths are needed, the new Fm+ no-offset bus buffers and switch from NXP overcome this limitation by allowing buses to be broken into segments or branches to isolate the bus capacitance into lower capacitive segments meeting I²C-bus specifications. Thus, the PCA9605 and PCA9646 enable I²C-based monitoring and control systems which can serve with hundreds of nodes and/or bus wiring lengths up to 1 km (0.62 miles) at lower frequencies. Designers can now consider running I²C communications over long distances, while using inexpensive commodity cabling such as CAT5 in enterprise computing applications such as servers and mass storage systems, and in industrial and automotive applications. The PCA9525 is useful in standard Fast-mode applications to isolate capacitance.

The PCA9525 and PCA9605 offer a simple capacitance isolating buffer for 2-wire I²C or SMBus buses, allowing buses to be broken into segments or branches to isolate the bus capacitance into lower capacitive segments with the PCA9605 supporting the higher capacitance limits of Fm+. According to the company, while all previous bus buffers have required some sort of offset to allow the device to determine which direction the bus was driving, the new no-offset bus buffers from NXP use the scoreboard method to control direction, and are interoperable with most other bus buffer devices on the I²C bus

The new no-offset devices from NXP work with I²C-bus (Standard-mode, Fast-mode), SMBus (standard and high power mode), and PMBus; the PCA9605 and PCA9646 also work with I²C Fast-mode Plus (Fm+).

Fast switching times allow operation in excess of 1 MHz, enabling use of faster peripherals. Hardware enable input disables the device, allowing bus segments to be disconnected to save power and reuse the same slave addresses over multiple I²C-bus segments. The no-offset bus buffer inputs follow the I²C-bus specification for Hysteresis which improves bus noise immunity.

Operating voltages range from 2.7 to 5.5V. The devices also have a very low supply current – for example, maximum 1µA in standby, typical 170µA operating for the PCA9525; as well as 4mA pull-down outputs on the PCA9525 and strong 30mA pull-down outputs on the PCA9605 and PCA9646.

"Simple, fast and flexible, NXP I²C technology has been at the heart of server computing designs since we first invented the I²C bus over 30 years ago. By enabling designers to drive robust I²C-bus signals over long distances through interconnects in electrically noisy environments, our no-offset bus buffers and switch open up exciting new possibilities for the I²C bus in enterprise computing, industrial automation and automotive applications," said Steve Blozis, International Product Marketing Manager, Interface Business Line, NXP Semiconductors.

The PCA9525, PCA9605 and PCA9646 are all available immediately in SO and TSSOP package options. Pricing varies by product and volume; the PCA9525D is available at US $0.76 per 1K units.

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