PCA9541 datasheet(20/30 Pages) PHILIPS

20 / 30 page

Philips Semiconductors

Product data sheet

PCA9541

2-to-1 I2C demultiplexer with interrupt logic and reset

2004 Oct 01

I2C commands are sent via the primary or back-up master and

either master can take command of the I2C-bus. Either master at

any time can gain control of the slave devices if the other master is

disabled or removed from the system. The failed master is isolated

from the system and will not affect communication between the

on-line master and the slave devices located on the cards.

For even higher reliability in multi-point backplane applications,

two dedicated masters can be used for every card as shown in

Figure 18.

SR02463

SCL0

SDA0

SCL1

SDA1

SCL0

SDA0

SCL1

SDA1

SCL0

SDA0

SCL1

SDA1

SCL0

SDA0

SCL1

SDA1

Figure 18. Very High Reliability Backplane Application

MASTERS WITH SHARED RESOURCES

Some masters may not be multi-master capable or some masters

may not work well together and continually lock up the bus. The

PCA9541 can be used to separate the masters, as shown in

Figure 19, but still allow shared access to slave devices, such as

Field Replaceable Unit (FRU) EEPROMs or temperature sensors.

PCA9541

SLAVE A0

SLAVE A1

SLAVE A2

MASTER A

PCA9541

SLAVE B0

SLAVE B1

SLAVE B2

MASTER B

MAIN

MASTER

SW02101

ASSEMBLY A

ASSEMBLY B

SDA/SCL

Figure 19. Masters with Shared Resources Application

GATEKEEPER MULTIPLEXER

The PCA9541/03 can act as a gatekeeper multiplexer in applications

where there are multiple I2C devices with the same fixed address

(e.g., EEPROMs with address of “Z” as shown in Figure 20)

connected in a multi-point arrangement to the same I2C-bus. Up to

16 hot swappable cards/devices can be multiplexed to the same bus

master by using one PCA9541/03 per card/device. Since each

PCA9541/03 has its own unique address (e.g., “A”, “B”, “C”, etc), the

EEPROMs can be connected to the master, one at a time, by

connecting one PCA9541/03 (Master 0 position) while keeping the

rest of the cards/devices isolated (off position).

The alternative, shown with dashed lines, is to use a PCA9548

1-to-8 channel switch on the master card and run 8 I2C-buses, one

to each EEPROM card, to multiplex the master to each card. The

number of card pins used is the same in either case, but there are 7

less pairs of SDA/SCL traces on the PC board if the PCA9541/03 is

used.

SW02099

Figure 20. Gatekeeper Multiplexer Application

BUS INITIALIZATION/RECOVERY

If the I2C-bus is hung, I2C devices without a hardware reset pin

(e.g., Slave 1 and 2 in Figure 21) can be isolated from the master by

the PCA9541/03. The PCA9541/03 disconnects the bus when it is

reset via the hardware reset line, restoring the master’s control of

the rest of the bus (e.g., Slave 0). The bus master can then

command the PCA9541/03 to send 9 clock pulses/ stop condition to

reset the downstream I2C devices before they are reconnected to

the master or leave the downstream devices isolated.

MASTER

SW02100

SLAVE 0

SLAVE 1

SLAVE 2

SDA/SCL

SDA

SCL

RESET

SLAVE

I2C-bus

Figure 21. Bus Initialization/Recovery Application

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