PCA9543ADRG4 datasheet(5/20 Pages) TI

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RESET Input

Power-On Reset

Voltage Translation

5.0

4.0

(V)

3.0

2.0

1.0

5.0

5.5

2.0

2.5

3.0

3.5

4.0

4.5

Min

Typ

Max

PCA9543A

TWO-CHANNEL I2C-BUS SWITCH

WITH INTERRUPT LOGIC AND RESET

SCPS169 – SEPTEMBER 2007

Table 2. Control Register Read (Interrupt)(1)

INT1

INT0

COMMAND

No interrupt on channel 0

Interrupt on channel 0

No interrupt on channel 1

Interrupt on channel 1

No channel selected; power-up/reset default state

(1)

Two interrupts can be active at the same time.

The RESET input can be used to recover the PCA9543A from a bus-fault condition. The registers and the I2C

state machine within this device initialize to their default states if this signal is asserted low for a minimum of tWL.

All channels also are deselected in this case. RESET must be connected to VCC through a pullup resistor.

When power is applied to VCC, an internal power-on reset holds the PCA9543A in a reset condition until VCC has

reached VPOR. At this point, the reset condition is released and the PCA9543A registers and I

2C state machine

are initialized to their default states, all zeroes, causing all the channels to be deselected. Thereafter, VCC must

be lowered below 0.2 V to reset the device.

The pass-gate transistors of the PCA9543A are constructed such that the VCC voltage can be used to limit the

maximum voltage that is passed from one I2C bus to another.

Figure 4. Vpass Voltage vs VCC

Figure 4 shows the voltage characteristics of the pass gate transistors (note that the graph was generated using

the data specified in Electrical Characteristics section of this data sheet). In order for the PCA9543A to act as a

voltage translator, the Vpass voltage should be equal to or lower than the lowest bus voltage. For example, if the

main bus is running at 5 V and the downstream buses are 3.3 V and 2.7 V, Vpass must be equal to or below 2.7 V

to effectively clamp the downstream bus voltages. As shown in Figure 4, Vpass(max) is at 2.7 V when the

PCA9543A supply voltage is 3.5 V or lower, so the PCA9543A supply voltage could be set to 3.3 V. Pullup

resistors then can be used to bring the bus voltages to their appropriate levels (see Figure 14).

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