This dual bidirectional I2C buffer is operational at 2.3-V to
The PCA9515A is a BiCMOS integrated circuit intended for I2C
bus and SMBus systems applications. The device contains two identical bidirectional open-drain
buffer circuits that enable I2C and similar bus systems to be extended
without degradation of system performance.
The PCA9515A buffers both the serial data (SDA) and serial clock (SCL) signals on the
I2C bus, while retaining all the operating modes and features of the
I2C system. This enables two buses of 400-pF bus capacitance to be
connected in an I2C application.
The I2C bus capacitance limit of 400 pF restricts the number
of devices and bus length. Using the PCA9515A enables the system designer to isolate two halves of
a bus, accommodating more I2C devices or longer trace lengths.
The PCA9515A has an active-high enable (EN) input with an internal pullup, which allows
the user to select when the repeater is active. This can be used to isolate a badly behaved slave
on power-up reset. It never should change state during an I2C operation,
because disabling during a bus operation hangs the bus, and enabling part way through a bus cycle
could confuse the I2C parts being enabled. The EN input should change
state only when the global bus and the repeater port are in an idle state, to prevent system
The PCA9515A also can be used to run two buses: one at 5-V interface levels and the other
at 3.3-V interface levels, or one at 400-kHz operating frequency and the other at 100-kHz operating
frequency. If the two buses are operating at different frequencies, the 100-kHz bus must be
isolated when the 400-kHz operation of the other bus is required. If the master is running at
400 kHz, the maximum system operating frequency may be less than 400 kHz, because of the delays
that are added by the repeater.
The PCA9515A does not support clock stretching across the repeater.
The output low levels for each internal buffer are approximately 0.5 V, but the input
voltage of each internal buffer must be 70 mV or more below the output low level, when the output
internally is driven low. This prevents a lockup condition from occurring when the input low
condition is released.
Two or more PCA9515A devices cannot be used in series. The PCA9515A design does not allow
this configuration. Because there is no direction pin, slightly different valid low-voltage levels
are used to avoid lockup conditions between the input and the output of each repeater. A valid low
applied at the input of a PCA9515A is propagated as a buffered low with a slightly higher value on
the enabled outputs. When this buffered low is applied to another PCA9515A-type device in series,
the second device does not recognize it as a valid low and does not propagate it as a buffered low
The device contains a power-up control circuit that sets an internal latch to prevent the
output circuits from becoming active until VCC is at a valid level
(VCC = 2.3 V).
As with the standard I2C system, pullup resistors are required
to provide the logic high levels on the buffered bus. The PCA9515A has standard open-collector
configuration of the I2C bus. The size of these pullup resistors depends
on the system, but each side of the repeater must have a pullup resistor. The device is designed to
work with Standard Mode and Fast Mode I2C devices in addition to SMBus
devices. Standard Mode I2C devices only specify 3 mA in a generic
I2C system where Standard Mode devices and multiple masters are
possible. Under certain conditions, high termination currents can be used.