CAT9554, CAT9554A
http://onsemi.com
5
SCL
SDA IN
SDA OUT
Figure 2. I
2
C Serial Interface Timing
t
SU:STA
t
AA
t
F
t
HD:STA
t
HD:DAT
t
LOW
t
DH
t
R
t
SU:DAT
t
LOW
t
HIGH
t
SU:STO
t
BUF
Pin Description
SCL: Serial Clock
The serial clock input clocks all data transferred into or out
of the device. The SCL line requires a pull−up resistor if it
is driven by an open drain output.
SDA: Serial Data/Address
The bidirectional serial data/address pin is used to transfer
all data into and out of the device. The SDA pin is an open
drain output and can be wire−ORed with other open drain or
open collector outputs. A pull−up resistor must be connected
from SDA line to V
CC
. The value of the pull−up resistor, R
P
,
can be calculated based on minimum and maximum values
from Figure 3 and Figure 4 (see Note).
A0, A1, A2: Device Address Inputs
These inputs are used for extended addressing capability.
The A0, A1, A2 pins should be hardwired to V
CC
or V
SS
.
When hardwired, up to eight CAT9554/9554As may be
addressed on a single bus system. The levels on these inputs
are compared with corresponding bits, A2, A1, A0, from the
slave address byte.
I/O
0
to I/O
7
: Input / Output Ports
Any of these pins may be configured as input or output.
The simplified schematic of I/O
0
to I/O
7
is shown in
Figure 5. When an I/O is configured as an input, the Q1 and
Q2 output transistors are off creating a high impedance input
with a weak pull−up resistor (typical 100 kW). If the I/O pin
is configured as an output, the push−pull output stage is
enabled. Care should be taken if an external voltage is
applied to an I/O pin configured as an output due to the low
impedance paths that exist between the pin and either V
CC
or V
SS
.
Figure 3. Minimum R
P
Value vs.
Supply Voltage
Figure 4. Maximum R
P
Value vs.
Bus Capacitance
V
CC
(V) C
BUS
(pF)
4.84.44.03.63.22.82.42.0
0
0.5
1.0
1.5
2.0
2.5
400350300200150100500
0
1
2
3
4
6
7
8
R
Pmin
(KW)
R
Pmax
(KW)
5.2 5.6
I
OL
= 3 mA @ V
OLmax
250
5
Fast Mode I
2
C Bus /
tr max − 300 ns
NOTE: According to the Fast Mode I
2
C bus specification, for bus capacitance up to 200 pF, the pull up device can be a resistor. For bus
loads between 200 pF and 400 pF, the pull−up device can be a current source (Imax = 3 mA) or a switched resistor circuit.
