Datasheet
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RESET Input
Power-On Reset
Voltage Translation
5.0
4.0
V (V)
CC
V (V)
pas
s
3.0
2.0
1.0
5.0 5.52.0 2.5 3.0 3.5 4.0 4.5
Min
Typ
Max
PCA9543A
TWO-CHANNEL I
2
C-BUS SWITCH
WITH INTERRUPT LOGIC AND RESET
SCPS169 – SEPTEMBER 2007
Table 2. Control Register Read (Interrupt)
(1)
D7 D6 INT1 INT0 D3 D2 B1 B0 COMMAND
0 No interrupt on channel 0
X X X X X X X
1 Interrupt on channel 0
0 No interrupt on channel 1
X X X X X X X
1 Interrupt on channel 1
0 0 0 0 0 0 0 0 No channel selected; power-up/reset default state
(1) Two interrupts can be active at the same time.
The RESET input can be used to recover the PCA9543A from a bus-fault condition. The registers and the I
2
C
state machine within this device initialize to their default states if this signal is asserted low for a minimum of t
WL
.
All channels also are deselected in this case. RESET must be connected to V
CC
through a pullup resistor.
When power is applied to V
CC
, an internal power-on reset holds the PCA9543A in a reset condition until V
CC
has
reached V
POR
. At this point, the reset condition is released and the PCA9543A registers and I
2
C state machine
are initialized to their default states, all zeroes, causing all the channels to be deselected. Thereafter, V
CC
must
be lowered below 0.2 V to reset the device.
The pass-gate transistors of the PCA9543A are constructed such that the V
CC
voltage can be used to limit the
maximum voltage that is passed from one I
2
C bus to another.
Figure 4. V
pass
Voltage vs V
CC
Figure 4 shows the voltage characteristics of the pass gate transistors (note that the graph was generated using
the data specified in Electrical Characteristics section of this data sheet). In order for the PCA9543A 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 is running at 5 V and the downstream buses are 3.3 V and 2.7 V, V
pass
must be equal to or below 2.7 V
to effectively clamp the downstream bus voltages. As shown in Figure 4, V
pass(max)
is at 2.7 V when the
PCA9543A supply voltage is 3.5 V or lower, so the PCA9543A supply voltage could be set to 3.3 V. Pullup
resistors then can be used to bring the bus voltages to their appropriate levels (see Figure 14 ).
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