PCA9618
Single channel Fm+ I2C-bus repeater
Rev. 1 — 13 January 2016
Product data sheet
1. General description
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 0.35VCC
.