Philips Semiconductors
Product data sheet
PCA9515A
I
2
C-bus repeater
2004 Sep 29
3
PCA9515A
V
CC
SDA1
SCL1
SCL0
SDA0
SW02244
PULL-UP
RESISTOR
EN
GND
Figure 2. PCA9515A block diagram
The output pull-down of each internal buffer is set for approximately
0.5 V, while the input threshold of each internal buffer is set about
0.07 V lower, when the output is internally driven LOW. This
prevents a lock-up condition from occurring.
FUNCTIONAL DESCRIPTION
The PCA9515A integrated circuit contains two identical buffer
circuits which enable I
2
C and similar bus systems to be extended
without degradation of system performance.
The PCA9515A contains two bi-directional, open drain buffers
specifically designed to support the standard LOW-level-contention
arbitration of the I
2
C-bus. Except during arbitration or clock
stretching, the PCA9515A acts like a pair of non-inverting, open
drain buffers, one for SDA and one for SCL.
Enable
The EN pin is active HIGH with an internal pull up and allows the
user to select when the repeater is active. This can be used to
isolate a badly behaved slave on power up until after the system
power up reset. It should never change state during an I
2
C
operation because disabling during a bus operation will hang the
bus and enabling part way through a bus cycle could confuse the
I
2
C parts being enabled.
The enable pin should only change state when the global bus and
the repeater port are in an idle state to prevent system failures.
I
2
C Systems
As with the standard I
2
C system, pull-up resistors are required to
provide the logic HIGH levels on the Buffered bus. (Standard
open-collector configuration of the I
2
C-bus). The size of these
pull-up resistors depends on the system, but each side of the
repeater must have a pull-up resistor. This part designed to work
with standard mode and fast mode I
2
C devices in addition to SMBus
devices. Standard mode I
2
C devices only specify 3 mA output drive,
this limits the termination current to 3 mA in a generic I
2
C system
where standard mode devices and multiple masters are possible.
Under certain conditions higher termination currents can be used.
Please see Application Note AN255 “I
2
C & SMBus Repeaters, Hubs
and Expanders”for additional information on sizing resistors and
precautions when using more than one PCA9515A/PCA9516A in a
system or using the PCA9515A/16A in conjunction with the P82B96.