PCA9541BS/03 View Datasheet(PDF) - NXP Semiconductors.

Part Name

Description

MFG CO.

PCA9541BS/03

2-to-1 I2C-bus master selector with interrupt logic and reset

NXP Semiconductors. 

NXP Semiconductors

PCA9541

2-to-1 I2C-bus master selector with interrupt logic and reset

8.6 External reset

A reset can be accomplished by holding the RESET pin LOW for a minimum of tw(rst)L. The

PCA9541 registers and I2C-bus state machine will be held in their default states until the

RESET input is once again HIGH. This input typically requires a pull-up resistor to VDD.

Default states are:

• I2C-bus upstream Channel 0 connected to the I2C-bus downstream channel for the

PCA9541/01

• no I2C-bus upstream channel connected to the I2C-bus downstream channel for the

PCA9541/03.

8.7 Voltage translation

The pass gate transistors of the PCA9541 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)

PCA9541_7

Product data sheet

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 8. Pass gate voltage as a function of supply voltage

Figure 8 shows the voltage characteristics of the pass gate transistors (note that the graph

was generated using the data specified in Section 12 “Static characteristics” of this data

sheet). In order for the PCA9541 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 5 V, and the downstream bus was 3.3 V, then Vo(sw) should be equal to or below

3.3 V to effectively clamp the downstream bus voltages. Looking at Figure 8, we see that

Vo(sw)(max) will be at 3.3 V when the PCA9541 supply voltage is 3.5 V or lower so the

PCA9541 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 17).

More Information on voltage translation can be found in Application Note AN262:

PCA954X family of I2C/SMBus multiplexers and switches.

Rev. 07 — 2 July 2009

© NXP B.V. 2009. All rights reserved.

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