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Product data sheet Rev. 9 — 5 May 2014 9 of 32

NXP Semiconductors

PCA9545A/45B/45C

4-channel I

C-bus switch with interrupt logic and reset

6.4 Power-on reset

When power is applied to V

, an internal Power-On Reset (POR) holds the

PCA9545A/45B/45C in a reset condition until V

has reached V

POR

. At this point, the

reset condition is released and the PCA9545A/45B/45C registers and I

C-bus state

machine are initialized to their default states (all zeroes) causing all the channels to be

deselected. Thereafter, V

must be lowered below 0.2 V for at least 5 s in order to reset

the device.

6.5 Voltage translation

The pass gate transistors of the PCA9545A/45B/45C are constructed such that the V

voltage can be used to limit the maximum voltage that is passed from one I

C-bus to

another.

Figure 9 shows the voltage characteristics of the pass gate transistors (note that the graph

was generated using the data specified in Section 11 “

Static characteristics” of this data

sheet). In order for the PCA9545A/45B/45C to act as a voltage translator, the V

o(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 V

o(sw)

should be equal to or below 2.7 V to clamp the downstream bus voltages effectively.

Looking at Figure 9

, we see that V

o(sw)(max)

is at 2.7 V when the PCA9545A/45B/45C

supply voltage is 3.5 V or lower, so the PCA9545A/45B/45C 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 16

More Information can be found in Application Note AN262: PCA954X family of I

C/SMBus

multiplexers and switches.

(1) maximum

(2) typical

(3) minimum

Fig 9. Pass gate voltage versus supply voltage

(V)

2.0 5.54.53.0 4.0

002aaa964

3.0

2.0

4.0

5.0

o(sw)

(V)

1.0

3.5 5.02.5

(1)

(2)

(3)