Datasheet

PCA9547 All information provided in this document is subject to legal disclaimers. © NXP Semiconductors N.V. 2014. All rights reserved.
Product data sheet Rev. 4 — 1 April 2014 8 of 30
NXP Semiconductors
PCA9547
8-channel I
2
C-bus multiplexer with reset
6.5 Voltage translation
The pass gate transistors of the PCA9547 are constructed such that the V
DD
voltage can
be used to limit the maximum voltage that will be passed from one I
2
C-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 11 “
Static characteristics” of this
data sheet). In order for the PCA9547 to act as a voltage translator, the V
o(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 V
o(mux)
should be
equal to or below 2.7 V to effectively clamp the downstream bus voltages. Looking at
Figure 7
, we see that V
o(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 I
2
C/SMBus
multiplexers and switches.
(1) maximum
(2) typical
(3) minimum
Fig 7. Pass gate voltage as a function of supply voltage
V
DD
(V)
2.0 5.54.53.0 4.0
002aab802
3.0
2.0
4.0
5.0
V
o(mux)
(V)
1.0
3.5 5.02.5
(1)
(2)
(3)