PD518 datasheet(10/20 Pages) TI

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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

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

100 kHz

400 kHz

GND

3.3 V or 5 V

PCA9518

DEVICE 2

PCA9518

DEVICE 1

SDA0

EXPSCL2

EXPSCL1

EN2

EN3

VCC

PCA9518

EXPANDABLE FIVE-CHANNEL I2C HUB

SCPS132A – JUNE 2006 – REVISED JULY 2007

Figure 3 shows an application in which the PCA9518 can be used.

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 VCC. SDA0 and SCL0 can be used as a

normal I2C port, but they must be pulled up to VCC if unused, because there is no enable pin.

Figure 3. Multiple Expandable Five-Channel I2C Hubs

Here, the system master is running on a 3.3-V I2C 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 I2C 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 VCC, the other

ports are pulled down to the VOL of the PCA9518, which is typically 0.5 V.

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