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General description

The PCA9541A is a 2-to-1 I2C-bus master selector designed for high reliability dual

master I2C-bus applications where system operation is required, even when one master

fails or the controller card is removed for maintenance. The two masters (for example,

primary and back-up) are located on separate I2C-buses that connect to the same

downstream I2C-bus slave devices. I2C-bus commands are sent by either I2C-bus master and are used to select one master at a time. 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 does not affect communication between the on-line master and the slave devices on the downstream I2C-bus.

Two versions are offered for different architectures. PCA9541A/01 with channel 0

selected at start-up, and PCA9541A/03 with no channel selected after start-up.

The interrupt outputs are used to provide an indication of which master has control of the bus. One interrupt input (INT_IN) collects downstream information and propagates it to the 2 upstream I2C-buses (INT0 and INT1) if enabled. INT0 and INT1 are also used to let the previous bus master know that it is not in control of the bus anymore and to indicate the completion of the bus recovery/initialization sequence. If the masking option is set, those interrupts can be disabled and do not generate an interrupt.

A bus recovery/initialization if enabled sends nine clock pulses, a not acknowledge, and a

STOP condition in order to set the downstream I2C-bus devices to an initialized state

before actually switching the channel to the selected master. An interrupt is sent to the upstream channel when the recovery/initialization procedure is completed. An internal bus sensor senses the downstream I2C-bus traffic and generates an interrupt if a channel switch occurs during a non-idle bus condition. This function is enabled when

the PCA9541A recovery/initialization is not used. The interrupt signal informs the master

that an external I2C-bus recovery/initialization must be performed. It can be disabled and an interrupt is not generated. The pass gates of the switches are constructed such that the VDD pin can be used to limit the maximum high voltage, which will be passed by the PCA9541A. This allows the use of different bus voltages on each pair, so that 1.8 V, 2.5 V, or 3.3 V devices can communicate with 5 V devices without any additional protection. The PCA9541A does not isolate the capacitive loading on either side of the device, so the designer must take into account all trace and device capacitances on both sides of the device, and pull-up resistors must be used on all channels. External pull-up resistors pull the bus to the desired voltage level for each channel. All I/O pins are 6.0 V tolerant.An active LOW reset input allows the PCA9541A to be initialized. Pulling the RESET pin LOW resets the I2C-bus state machine and configures the device to its default state as does the internal Power-On Reset (POR) function.

Features and benefits

? 2-to-1 bidirectional master selector

? I2C-bus interface logic; compatible with SMBus standards

? PCA9541A/01 powers up with Channel 0 selected

? PCA9541A/03 powers up with no channel selected and either master can take control

of the bus

? Active LOW interrupt input

? 2 active LOW interrupt outputs

? Active LOW reset input

? 4 address pins allowing up to 16 devices on the I2C-bus

? Channel selection via I2C-bus

? Bus initialization/recovery function

? Bus traffic sensor

? Low Ron switches

? Allows voltage level translation between 1.8 V, 2.5 V, 3.3 V and 5 V buses

? No glitch on power-up

? Supports hot insertion

? Software identical for both masters

? Low standby current

? Operating power supply voltage range of 2.3 V to 5.5 V

? 6.0 V tolerant inputs

? 0 Hz to 400 kHz clock frequency

? ESD protection exceeds 2000 V HBM per JESD22-A114 and 1000 V CDM per

JESD22-C101

? Latch-up testing is done to JEDEC Standard JESD78 which exceeds 100 mA

? Packages offered: SO16, TSSOP16, HVQFN16