INTEGRATED CIRCUITS
APPLICATION NOTE
AN262_2
PCA954X FAMILY OF I²C / SMBus MULTIPLEXERS
and SWITCHES
PCA9540B, PCA9541, PCA9542A, PCA9543A, PCA9544A, PCA9545A,
PCA9546A, PCA9547, PCA9548A, PCA9549
Abstract
-
Philips Semiconductors family of Multiplexers and Switches are detailed in this application note that
discusses device operation, software programming, pull up resistor sizing/bus termination and typical
applications.
Paul Boogaards -
Field Application Engineer
Jean-Marc Irazabal -
PCA Technical Marketing Manager
Steve Blozis -
PCA International Product Manager
Specialty Logic Product Line
Logic Product Group
Philips Semiconductors
1
October 27, 2004
TABLE OF CONTENTS
TABLE OF CONTENTS ...................................................................................................................................................2
OVERVIEW .......................................................................................................................................................................3
D
ESCRIPTION
.....................................................................................................................................................................3
A
PPLICATIONS
...................................................................................................................................................................3
F
EATURES
.........................................................................................................................................................................3
O
PERATING
C
HARACTERISTICS
.........................................................................................................................................4
D
EVICE
P
INOUT
.................................................................................................................................................................5
O
RDERING
I
NFORMATION
..................................................................................................................................................6
D
ATA
S
HEETS AND
IBIS M
ODELS
.....................................................................................................................................6
TECHNICAL INFORMATION .......................................................................................................................................6
B
LOCK
D
IAGRAM
PCA954
X DEVICES
(E
XCEPT
PCA9541
AND
PCA9549) ......................................................................6
B
LOCK
D
IAGRAM
PCA9541..............................................................................................................................................8
B
LOCK
D
IAGRAM
PCA9549..............................................................................................................................................9
I²C C
OMMUNICATIONS
......................................................................................................................................................9
I
NTERRUPTS
....................................................................................................................................................................11
C
OMMAND
S
EQUENCING
.................................................................................................................................................13
P
OWER UP
/ R
ESET DEFAULT STATE
................................................................................................................................13
V
OLTAGE
C
LAMPING
......................................................................................................................................................13
V
OLTAGE
T
RANSLATION
.................................................................................................................................................14
H
OW TO USE THE
PCA9541
AS A
2-
CHANNEL MULTIPLEXER
..........................................................................................15
D
ETERMINING
P
ULL
-U
P
R
ESISTORS VALUES
...................................................................................................................15
APPLICATIONS..............................................................................................................................................................19
I
2
C M
ULTIPLEXING
.........................................................................................................................................................19
V
OLTAGE
L
EVEL
S
HIFTING
.............................................................................................................................................19
C
APACITIVE
L
OAD
S
HARING
...........................................................................................................................................19
T
YPICAL
A
PPLICATION
....................................................................................................................................................20
FREQUENTLY ASKED QUESTIONS .........................................................................................................................20
ADDITIONAL INFORMATION ...................................................................................................................................26
REVISION HISTORY.....................................................................................................................................................26
2
OVERVIEW
Description
The Philips family of Multiplexers and Switches consists of bi-directional translating switches controlled via the I
2
C or
SMBus to fan out an upstream SCL/SDA pair to 2, 4 or 8 downstream channels of SCx/SDx pairs. The Multiplexers
allow only one downstream channel to be selected at a time, while the Switches allow any individual downstream
channel or combination of downstream channels to be selected, depending on the content of the programmable control
register. Once one or several channels have been selected, the device acts as a wire, allowing the master on the upstream
channel to send commands to devices on all the active downstream channels, and devices on the active downstream
channels to communicate with each other and the master. External pull-up resistors are used to pull each individual
channel up to the desired voltage level. Combined interrupt output and hardware reset input are device options that are
featured.
MULTIPLEXER
I C Bus
Interrupt
Out
I
2
C
Controller
2
SWITCH
I
2
C Bus 0
I
2
C Bus
Reset
Interrupt
Out
IC
Controller
2
I
2
C Bus 0
OFF
OFF
I C Bus 1
Interrupt 0
Interrupt 1
2
I
2
C Bus 1
OFF
Interrupt 0
Interrupt 1
Applications
These devices can be used for a wide variety of applications:
I
2
C Multiplexing
- Some specialized devices only have one I
2
C or SMBus address and sometimes several identical
devices are needed in the same system. The multiplexers and switches split the I
2
C bus into several sub-branches and
allow the I
2
C master to select and address one of multiple identical devices, in order to resolve address conflict issues.
Voltage Level Shifting
- Many I
2
C and SMBus devices operate at different voltage levels but need to operate on a
common bus. The multiplexers and switches allow translation between 1.65 V and 5.5 V. So, for example, a 5 V I
2
C
master on the upstream channel can communicate with a 3.3 V (non 5 V tolerant) SMBus device on channel 0 and a
2.5 V I
2
C device on channel 1. The channel pass gates are constructed such that the V
DD
pin can be used to limit the
maximum high voltage that will be passed by the device. This allows the use of different bus voltages on each pair, so
that 1.8 V or 2.5 V or 3.3 V devices can communicate with 5 V devices without any additional protection. All I/O pins
are tolerant up to 6.0 V. The Switches are best for this application since multiple downstream channels can be active at
the same time.
Capacitive Load Sharing
- Adding more I
2
C and SMBus devices on the bus may exceed the 400 pF limitation. The
multiplexers and switches can isolate devices that are not currently needed to reduce the overall system loading and
maintain the total system load below 400 pF. When active, the channels act as a wire and the cumulative capacitive
loading of the upstream channel and all active downstream channels must be considered.
Features
Interrupt Function
- Interrupt inputs, one for each of the downstream channels, are provided as an option on both the
Multiplexers and Switches. The single interrupt output acts as an OR of the interrupt inputs and is not latched.
Hardware Reset
- An external active low hardware reset pin (/RESET) is provided on the Switches in addition to the
Power On Reset (POR) feature found on both the Multiplexers and Switches. Either /RESET or POR resets the
downstream channels to the default state of no channels selected. The reset feature is useful should a downstream device
3
lock up the bus and the master loses the ability to communicate. The master can use the reset to restore communication
within the upstream channel and then selectively restore communication with the downstream channels without having
to cycle power to the equipment or to other I
2
C bus devices. The PCA9541 option /01 and /02 and the PCA9547 have
one channel active at start up for applications that want a connection without having to address the multiplexer.
Hardware Pins
- Up to three hardware pins (A0, A1, A2), except the PCA9541 that has an additional pin (A3), are
provided to change the I
2
C address and allow up to eight PCA954X devices (up to sixteen for the PCA9541) to share the
same I
2
C/SMBus.
MULTIPLEXER (In/Out)
FEATURES
PACKAGES
SO (narrow)
PIN COUNT
INTERRUPT (In/Out)
HARDWARE RESET
SWITCH (In/Out)
# of ADDRESSES
DEVICE NAME
SO (wide)
PCA9540B
PCA9541
PCA9542A
PCA9543A
PCA9544A
PCA9545A
PCA9546A
PCA9547
PCA9548A
PCA9549
1-2
2-1
1-2
1-4
1-8
1
8
16
1-2
16
8
2-1
14
1-2
4
2-1
14
8
4-1
20
1-4
4
4-1
20
1-4
8
16
8
24
1-8
8
24
8-bit
8
24
Table 1. PCA954X Features
D
D
D
D
D
D
D
D
D
D
DP
PW
PW
PW
PW
PW
PW
PW
PW
PW
BS
BS
BS
BS
BS
BS
BS
Operating Characteristics
2.3 V to 5.5 V operating voltage
2
•
6.0 V tolerant I C I/Os
•
0 kHz to 400 kHz operating frequency
•
-40 ºC to 85 ºC operating temperature range
2
•
I C and SMBus compatible
•
ESD protection exceeds:
•
2000 V HBM per JESD22-A114
•
200 V MM per JESD22-A115
•
1000 V CDM per JESD22-C101
•
JEDEC Standard JESD78 Latch-up testing exceeds 100 mA
•
Manufactured in high volume BiCMOS process
•
4
HVQFN
TSSOP
Device Pinout
2-Channel
PCA9540B
2-Channel
w/Interrupt
PCA9542A
4-Channel
w/Interrupt
PCA9544A
4-Channel
8-Channel
PCA9547
M
U
L
T
I
P
L
E
X
E
R
PCA9541
With Reset
PCA9543A
PCA9545A
PCA9546A
With Reset
PCA9548A / PCA9549
S
W
I
T
C
H
With Reset
With Reset
With Reset
With Reset
Table 2. PCA954X Pin Out
5
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