Unstuck bus

Linear Technology Corporation

has introduced the LTC4303 and LTC4304 2-wire bus buffers with stuck bus recovery. These new ICs are said to solve the common problem of a stuck bus by isolating all of the bus connections on the upstream side, while restoring the downstream bus. If the serial data output SDAOUT or serial clock output SCLOUT are low for more than 30ms, the LTC4304 will automatically break the data and clock connections, issuing a Fault signal.

Sequentially, the LTC4304 will automatically generate up to 16 clock pulses on the SCLOUT in an attempt to free the bus. When the bus becomes free, a connection is immediately enabled and proper operation resumes. With stuck bus recovery, the LTC4303 and LTC4304 eliminate the need for a general system reset and unburden the microcontroller, providing the appropriate signals to free the bus.

The LTC4303 and LTC4304 also provide capacitive isolation between the backplane and the card’s I2C busses, even if their respective supplies are at different levels. The ICs perform this level translation without the need of a second supply pin or a second pair of input pull-up resistors, eliminating the requirement to dedicate a connector pin for the backplane supply voltage.

Due to the capacitive buffering, the backplane bus sees only the capacitance of the buffer ICs, about 10pF each, instead of seeing the entire cards’ bus capacitance. This increases the number of nodes that can be supported in a given system and eliminates most signal integrity problems.

In addition to facilitating live card insertion or removal, the LTC4303 and LTC4304’s SDA and SCL pins withstand ±15kV ESD, protecting the card from damage due to handling. The part greatly simplifies the utilisation of an I2C bus to manage a large number of cards with different supply and bus voltage levels in network server, desktop PC or telecom environments.

The LTC4303 is offered in MSOP-8 and 3mm x 3mm DFN packages and is pin-compatible with the LTC4300A-1. The LTC4304 is available in MSOP-10 and 3mm x 3mm DFN packages. Both ICs are specified over the commercial and industrial temperature ranges and pricing starts at $2.10 each for 1,000 piece quantities.