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PA9542A

2-channel I2C multiplexer and interrupt logic

Philips Electronics 

Philips Semiconductors

2-channel I2C multiplexer and interrupt logic

Product data sheet

PCA9542A

VOLTAGE TRANSLATION

The pass gate transistors of the PCA9542A are constructed such

that the VDD voltage can be used to limit the maximum voltage that

will be passed from one I2C-bus to another.

5.0

4.5

4.0

3.5

Vpass

3.0

2.5

2.0

1.5

1.0

2.0

Vpass vs. VDD

MAXIMUM

TYPICAL

2.5

3.0

3.5

4.0

VDD

MINIMUM

4.5

5.0

5.5

SW00820

Figure 5. Vpass voltage

Figure 5 shows the voltage characteristics of the pass gate

transistors (note that the graph was generated using the data

specified in the DC Characteristics section of this datasheet). In

order for the PCA9542A 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 was running at 5 V, and the downstream

buses were 3.3 V and 2.7 V, then Vpass should be equal to or below

2.7 V to effectively clamp the downstream bus voltages. Looking at

Figure 5, we see that Vpass (max.) will be at 2.7 V when the

PCA9542A supply voltage is 3.5 V or lower so the PCA9542A

supply voltage could be set to 3.3 V. Pull-up resistors can then be

used to bring the bus voltages to their appropriate levels (see Figure

12).

More Information can be found in Application Note AN262 PCA954X

family of I2C/SMBus multiplexers and switches.

2004 Sep 29

5

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