PCA9546 datasheet(6/17 Pages) PHILIPS

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Philips Semiconductors

Product data sheet

PCA9546

4-channel I2C switch with reset

2004 Sep 30

VOLTAGE TRANSLATION

The pass gate transistors of the PCA9546 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

3.0

2.5

2.0

1.5

1.0

Vpass vs. VDD

2.5

3.0

3.5

4.0

4.5

5.0

5.5

Vpass

VDD

MINIMUM

TYPICAL

MAXIMUM

SW00820

2.0

Figure 5. Vpass voltage vs. VDD

Figure 5 shows the voltage characteristics of the pass gate

transistors (note that the PCA9546 is only tested at the points

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

order for the PCA9546 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

PCA9546 supply voltage is 3.5 V or lower so the PCA9546 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.

PCA9546 Datasheet(PDF) 6 Page - NXP Semiconductors

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