PCA9618UK: Single channel Fm+ I²C-bus repeater

The PCA9618 is a CMOS integrated circuit that provides Fast-mode Plus (Fm+) I²C-bus or SMBus buffering of either the SCL or SDA line or can be used in any single bit applications that require buffering. While retaining all the operating modes and features of the I²C-bus system, it also permits extension of the I²C-bus by providing bidirectional buffering, thus enabling buses of 540 pF at 1 MHz or up to 4000 pF at lower speeds. Using the PCA9618 enables the system designer to isolate two halves of a bus for capacitance. The DATAA and DATAB pins are overvoltage tolerant and are high-impedance when the PCA9618 is unpowered.

The PCA9618 can be used to delay the SDA path by at least the minimum propagation delay, thereby providing an effective data hold time for applications that require an SDA hold time with respect to SCL. The PCA9618 includes an internal glitch filter, so that it will ignore glitches rather than expand them, this also means that the minimum propagation delay is on the order of 46 ns and is reasonably stable over temperature and supply voltage. Although this is not sufficient to provide the SDA delay requirement of the SMBus hold time specification of 300 ns, many parts that cannot be used with the 0 ns hold time of the I2C-bus specification only require a few ns of hold time to work correctly in a system. For these applications, the PCA9618 is an effective solution.

The PCA9618 can also be used as a buffer on a 1-wire bus similar to how the PCA9617A is used for the I²C-bus or to buffer the master (microcontroller’s I/O) if the master’s output is not strong enough to drive the 1-wire bus.

The 2.2 V to 5.5 V bus port B driver has the static level offset, while the port A driver eliminates the static offset voltage. This results in a LOW on the port B translating into a nearly 0 V LOW on the port A. This static offset voltage prevents the PCA9618 from latching into a steady state LOW when driven LOW.

The static offset design of the port B PCA9618 I/O driver prevents it from being connected to the static or incremented offset sides of other bus buffers. Port A of two or more PCA9618s can be connected together, also, to allow a star topography with port A on the common bus. Port A can be connected directly to any other buffer with static or incremented offset outputs. Multiple PCA9618s can be connected in series, port A to port B, with no build-up in offset voltage with only time of flight delays to consider.

The output pull-down on the port B internal buffer LOW is set for approximately 0.55 V, while the input threshold of the internal buffer is set about 90 mV lower (0.45 V). When the port B I/O is driven LOW internally, the LOW is not recognized as a LOW by the input. This prevents a latching condition from occurring. The output pull-down on port A drives a hard LOW and the input level is set at 0.35V_CC.