Hot swap I2C multiplexers provide capacitive buffering supercapacitors
December 16, 2010 // Paul Buckley
Linear Technology Corporation has introduced the LTC4312 and LTC4314 2-wire bus multiplexers, which provide individual enable pins to connect an upstream I2C bus to any combination of downstream busses or cards. The LTC4312 and LTC4314 are pin-selectable multiplexers with bus buffers that reduce component count while promoting ideal I2C signal integrity.
The LTC4312 multiplexes two channels, while the LTC4314 multiplexes four channels. These devices allow easy I2C address expansion, providing the ability to address one of multiple identical devices, thus resolving address conflict issues. Bidirectional capacitive buffering allows extension of the I2C bus size well beyond the 400 pF I2C bus specification and prevents I2C signal corruption during live board insertion or removal.
The LTC4312 and LTC4314 are suitable for a wide range of applications, including radial architectures in telecommunications systems such as ATCA, address expansion and level translators. Many I2C and SMBus devices operate at different supply voltage levels, yet must communicate in the same application.
The LTC4312 and LTC4314 supports level translation for bus voltages ranging from 1.5 V to 5.5 V. The devices provide the ability to power devices from different supply voltages while maintaining fully bidirectional communications between all devices in the system. Bidirectional buffering keeps backplane and card capacitances isolated, while maintaining low offsets and high noise margins up to 0.3 VCC. In addition, built-in rise time accelerators provide strong pull-up currents on SCL and SDA rising edges to meet I2C rise time specifications for heavily loaded busses; the strength of these accelerators can be selected or disabled completely.
Safety measures include a stuck bus disconnect and recovery feature to disengage the input from all enabled output channels and issue clocks to the stuck device, a fault output to signal when the host a bus is stuck low, and ±4 kV HBM ESD protection for increased ruggedness.
Availability and Pricing
The LTC4312 is available in 14-lead 4 mm x 3 mm DFN and 16-lead SSOP packages, and the LTC4314 is available in 20-lead 3 mm x 4 mm QFN and 20-lead SSOP packages. Offered over the commercial and industrial temperature ranges, pricing for the LTC4312 and LTC4314 starts at $1.95 and $2.65 each, respectively for 1000-piece quantities.
For more information visit www.linear.com/4312 and www.linear.com/4314
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