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參數(shù)資料
| 型號： | 935270442112 |
| 廠商： | NXP SEMICONDUCTORS |
| 元件分類： | 編、解碼器及復(fù)用、解復(fù)用 |
| 英文描述： | 2 LINE TO 1 LINE MULTIPLEXER, TRUE OUTPUT, PDSO20 |
| 封裝： | 4.40 MM, PLASTIC, MO-153, SOT-360-1, TSSOP-20 |
| 文件頁數(shù)： | 14/17頁 |
| 文件大小： | 144K |
| 代理商： | 935270442112 |
Philips Semiconductors
Product data
PCA9545
4-channel I2C switch with interrupt logic and reset
2002 Dec 13
6
INTERRUPT HANDLING
The PCA9545 provides 4 interrupt inputs, one for each channel, and
one open drain interrupt output. When an interrupt is generated by any
device, it will be detected by the PCA9545 and the interrupt output
will be driven LOW. The channel does not need to be active for
detection of the interrupt. A bit is also set in the control register.
Bits 4 - 7 of the control register correspond to channels 0 - 3 of the
PCA9545, respectively. Therefore, if an interrupt is generated by any
device connected to channel 1, the state of the interrupt inputs is
loaded into the control register when a read is accomplished.
Likewise, an interrupt on any device connected to channel 0 would
cause bit 4 of the control register to be set on the read. The master
can then address the PCA9545 and read the contents of the control
register to determine which channel contains the device generating the
interrupt. The master can then reconfigure the PCA9545 to select this
channel, and locate the device generating the interrupt and clear it.
It should be noted that more than one device can be providing an
interrupt on a channel, so it is up to the master to ensure that all
devices on a channel are interrogated for an interrupt.
The interrupt inputs may be used as general purpose inputs if the
interrupt function is not required.
If unused, interrupt input(s) must be connected to VDD through a
pull-up resistor.
Table 2. Control Register Read — Interrupt
INT3
INT2
INT1
INT0
B3
B2
B1
B0
COMMAND
0
No interrupt
on channel 0
X
1
X
Interrupt on
channel 0
0
No interrupt
on channel 1
X
1
X
Interrupt on
channel 1
0
No interrupt
on channel 2
X
1
X
Interrupt on
channel 2
0
No interrupt
on channel 3
1
X
Interrupt on
channel 3
NOTE: Several interrupts can be active at the same time.
Ex: INT3 = 0, INT2 = 1, INT1 = 1, INT0 = 0, means that there is no
interrupt on channels 0 and 3, and there is interrupt on channels 1
and 2.
RESET INPUT
The RESET input is an active-LOW signal which may be used to
recover from a bus fault condition. By asserting this signal LOW for
a minimum of tWL, the PCA9545 will reset its registers and I2C state
machine and will deselect all channels. The RESET input must be
connected to VDD through a pull-up resistor.
POWER-ON RESET
When power is applied to VDD, an internal Power On Reset holds
the PCA9545 in a reset state until VDD has reached VPOR. At this
point, the reset condition is released and the PCA9545 registers and
I2C state machine are initialized to their default states, all zeroes
causing all the channels to be deselected.
VOLTAGE TRANSLATION
The pass gate transistors of the PCA9545 are constructed such that
the VDD 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
3.0
2.5
2.0
1.5
1.0
Vpass vs. VDD
2.5
3.0
3.5
4.0
4.5
5.0
5.5
Vpass
VDD
MINIMUM
TYPICAL
MAXIMUM
SW00820
2.0
Figure 6. Vpass voltage vs. VDD
Figure 6 shows the voltage characteristics of the pass gate
transistors (note that the graph was generated using the data
specified in the DC Characteristics section of this datasheet). In
order for the PCA9545 to act as a voltage translator, the Vpass
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 Vpass should be equal to or below
2.7 V to effectively clamp the downstream bus voltages. Looking at
Figure 6, we see that Vpass (max.) will be at 2.7 V when the
PCA9545 supply voltage is 3.5 V or lower so the PCA9545 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 13).
More Information can be found in Application Note AN262 PCA954X
family of I2C/SMBus multiplexers and switches.
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