Datasheet

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APPLICATION INFORMATION
BUS
MASTER
SUBSYSTEM 1
SDA
SDA0
SDA
SCL
SCL0
SCL
EN1
3.3 V
5 V
SDA1
SCL1
EN2
EN3
EN4
SDA
SCL
3.3 V
SDA2
SCL2
SDA
SCL
5 V
SDA3
SCL3
SDA
SCL
3.3 V
SDA4
SCL4
SCL0
EN1
SDA1
SCL1
EN4
SDA2
SCL2
SDA3
SCL3
SDA4
SCL4
EXPSDA2
EXPSDA2
EXPSCL1
EXPSCL1
SUBSYSTEM 2
SUBSYSTEM 3
SUBSYSTEM 4
SUBSYSTEM 5
SDA
SCL
5 V
SDA
SCL
3.3 V
SUBSYSTEM 6
Disabled
Not Connected
100 kHz
400 kHz
400 kHz
400 kHz
100 kHz
100 kHz
400 kHz
GND
GND
3.3 V or 5 V
3.3 V or 5 V
PCA9518
DEVICE 2
PCA9518
DEVICE 1
SDA0
EXPSCL2
EXPSCL2
EXPSCL1
EXPSCL1
EN2
EN3
V
CC
V
CC
PCA9518
EXPANDABLE FIVE-CHANNEL I
2
C HUB
SCPS132A – JUNE 2006 – REVISED JULY 2007
Figure 3 shows an application in which the PCA9518 can be used.
A. Only two of the five channels of the PCA9518 device 2 are being used. EN3 and EN4 are connected to GND to
disable channels 3 and 4, or SDA3/SCL3 and SDA4/SCL4 are pulled up to V
CC
. SDA0 and SCL0 can be used as a
normal I
2
C port, but they must be pulled up to V
CC
if unused, because there is no enable pin.
Figure 3. Multiple Expandable Five-Channel I
2
C Hubs
Here, the system master is running on a 3.3-V I
2
C bus, while the slaves are connected to a 3.3-V or 5-V bus.
The PCA9518 is 5-V tolerant, so it does not require any additional circuitry to translate between the different bus
voltages.
All buses run at 100 kHz, unless slaves 3, 4, and 5 are isolated from the bus. If the master bus and slaves 1, 2,
and 6 need to run at 400 kHz, slaves 3, 4, and 5 can be isolated through the bus master. In this case, the bus
master will change the state on the corresponding EN pin (for slaves 3, 4, and 5) to low.
Any segment of the hub can talk to any other segment of the hub. Bus masters and slaves can be located on
any segment with 400-pF load allowed on each segment.
When one port of the PCA9518 is pulled low by a device on the I
2
C bus, a CMOS hysteresis-type input detects
the falling edge and drives the EXPxxx1 line low; when the EXPxxx1 voltage is less than 0.5-V V
CC
, the other
ports are pulled down to the V
OL
of the PCA9518, which is typically 0.5 V.
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