PCA9641PW datasheet(12/55 Pages) NXP

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PCA9641

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Product data sheet

Rev. 2.1 — 27 October 2015

12 of 55

NXP Semiconductors

PCA9641

2-channel I2C-bus master arbiter

7.7 Voltage translation

The pass gate transistors of the PCA9641 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 graph

was generated using the data specified in Section 18 “Static characteristics” of this data

sheet). In order for the PCA9641 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 buses were

running at 3.3 V, and the downstream bus was 2.5 V, then Vo(sw) should be equal to or

below 2.5 V to effectively clamp the downstream bus voltages. Looking at Figure 7, we

see that Vo(sw)(max) will be at 2.5 V when the PCA9641 supply voltage is 3.375 V or lower

so the PCA9641 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 20).

More Information on voltage translation 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

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