Datasheet
PCA9541A All information provided in this document is subject to legal disclaimers. © NXP Semiconductors N.V. 2014. All rights reserved.
Product data sheet Rev. 5 — 24 April 2014 18 of 45
NXP Semiconductors
PCA9541A
2-to-1 I
2
C-bus master selector with interrupt logic and reset
7.6 External reset
A reset can be accomplished by holding the RESET pin LOW for a minimum of t
w(rst)L
.
The PCA9541A registers and I
2
C-bus state machine are held in their default states until
the RESET
input is once again HIGH. This input typically requires a pull-up resistor to
V
DD
.
Default states are:
• I
2
C-bus upstream Channel 0 connected to the I
2
C-bus downstream channel for the
PCA9541A/01
• no I
2
C-bus upstream channel connected to the I
2
C-bus downstream channel for the
PCA9541A/03.
7.7 Voltage translation
The pass gate transistors of the PCA9541A are constructed such that the V
DD
voltage can
be used to limit the maximum voltage that is passed from one I
2
C-bus to another.
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 PCA9541A 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 buses were
running at 5 V, and the downstream bus was 3.3 V, then V
o(sw)
should be equal to or
below 3.3 V to effectively clamp the downstream bus voltages. Looking at Figure 8
, we
see that V
o(sw)(max)
is at 3.3 V when the PCA9541A supply voltage is 4.0 V or lower so the
PCA9541A 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 I
2
C/SMBus multiplexers and switches.
(1) maximum
(2) typical
(3) minimum
Fig 8. Pass gate voltage as a function of supply voltage
V
DD
(V)
2.0 5.54.53.0 4.0
002aaa964
3.0
2.0
4.0
5.0
V
o(sw)
(V)
1.0
3.5 5.02.5
(1)
(2)
(3)