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PCA9542A

2-channel I2C-bus multiplexer and interrupt logic

NXP Semiconductors. 

NXP Semiconductors

PCA9542A

2-channel I2C-bus multiplexer and interrupt logic

6.5 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

Vo(sw)

(V)

4.0

3.0

2.0

002aaa964

(1)

(2)

(3)

1.0

2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5

VDD (V)

(1) maximum

(2) typical

(3) minimum

Fig 6. Pass gate voltage versus supply voltage

Figure 6 shows the voltage characteristics of the pass gate transistors (note that the graph

was generated using the data specified in Section 11 “Dynamic characteristics” of this

data sheet). In order for the PCA9542A to act as a voltage translator, the Vo(sw) 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 Vo(sw) should be

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

Figure 6, we see that Vo(sw)(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 13).

More Information can be found in Application Note AN262, PCA954X family of I2C/SMBus

multiplexers and switches.

PCA9542A_3

Product data sheet

Rev. 03 — 24 November 2008

© NXP B.V. 2008. All rights reserved.

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