PCA9547 datasheet(8/26 Pages) TI

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PCA9547_2

Product data sheet

Rev. 02 — 12 September 2006

8 of 26

Philips Semiconductors

PCA9547

8-channel I2C-bus multiplexer with reset

6.5 Voltage translation

The pass gate transistors of the PCA9547 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.

Figure 7 shows the voltage characteristics of the pass gate transistors (note that the

PCA9547 is only tested at the points speciﬁed in Section 10 “Static characteristics” of this

data sheet). In order for the PCA9547 to act as a voltage translator, the Vo(mux) 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(mux) should be

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

Figure 7, we see that Vo(mux)(max) will be at 2.7 V when the PCA9547 supply voltage is

3.5 V or lower so the PCA9547 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 14).

More information can be found in

Application Note AN262, PCA954X family of I2C/SMBus

multiplexers and switches.

(1) maximum

(2) typical

(3) minimum

Fig 7.

Pass gate voltage as a function of supply voltage

VDD (V)

2.0

5.5

4.5

3.0

4.0

002aab802

3.0

2.0

4.0

5.0

Vo(mux)

(V)

1.0

3.5

5.0

2.5

(1)

(2)

(3)

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