PCA9548 Datasheet, PDF (6/16 Pages) NXP Semiconductors – 8-channel I2C switch with reset

Philips Semiconductors
8-channel I²C switch with reset
Product data sheet
PCA9548
VOLTAGE TRANSLATION
The pass gate transistors of the PCA9548 are constructed such that
the V_DD voltage can be used to limit the maximum voltage that will
be passed from one I²C-bus to another.
5.0
4.5
4.0
3.5
V_pass
3.0
2.5
2.0
1.5
1.0
2.0
V_pass vs. V_DD
MAXIMUM
TYPICAL
2.5
3.0
3.5
4.0
V_DD
MINIMUM
4.5
5.0
5.5
SW00820
Figure 5 shows the voltage characteristics of the pass gate
transistors (note that the PCA9548 is only tested at the points
specified in the DC Characteristics section of this datasheet). In
order for the PCA9548 to act as a voltage translator, the V_pass
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_pass should be equal to or below
2.7 V to effectively clamp the downstream bus voltages. Looking at
Figure 5, we see that V_pass (max.) will be at 2.7 V when the
PCA9548 supply voltage is 3.5 V or lower so the PCA9548 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 12).
More Information can be found in Application Note AN262 PCA954X
family of I²C/SMBus multiplexers and switches.
Figure 5. V_pass voltage vs. V_DD
2004 Sep 30
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